阅读说明：本技术 一种自校准的高精度数字时间转换电路 (Self-calibration high-precision digital time conversion circuit ) 是由 申人升 周滔 常玉春 王志硕 刘宇帆 叶伟成 张璐 李技烨 刘炯晗 周义喆 牛仕 于 2021-07-26 设计创作，主要内容包括：本发明提供一种自校准的高精度数字时间转换电路。本发明包括：数字模拟转换器DAC、电容阵列、由多个开关组成的开关阵列及反相器；数字模拟转换器DAC连接电容阵列；电容阵列与反相器相连；反相器连接输出端；数字模拟转换器DAC、电容阵列、反相器及接地端分别设有开关；电容阵列,包括固定容值电容cap和可变容值电容cap＿vary；数字模拟转换器DAC根据输入的代表时间延迟的数字控制字对电容阵列进行充电,并将基准电流源的电流变化反馈给可变电容cap＿vary,从而对电容阵列的电容值进行补偿校准；反相器根据补偿校准后的电容阵列的电容值输出时钟信号。解决了现有技术中,基准电流受温度、工艺、电压变化的影响,导致输出时钟信号发生越位偏移的技术问题。(The invention provides a self-calibration high-precision digital time conversion circuit. The invention comprises the following steps: the digital-to-analog converter comprises a digital-to-analog converter DAC, a capacitor array, a switch array consisting of a plurality of switches and an inverter; the digital-to-analog converter DAC is connected with the capacitor array; the capacitor array is connected with the phase inverter; the inverter is connected with the output end; the DAC, the capacitor array, the phase inverter and the grounding end are respectively provided with a switch; the capacitor array comprises a fixed capacitance value capacitor cap and a variable capacitance value capacitor cap _ vary; the digital-to-analog converter DAC charges the capacitor array according to the input digital control word representing time delay, and feeds back the current change of the reference current source to the variable capacitor cap _ vary, so as to compensate and calibrate the capacitance value of the capacitor array; and the inverter outputs a clock signal according to the capacitance value of the capacitor array after compensation calibration. The technical problem that in the prior art, the output clock signal is subjected to offside offset due to the fact that the reference current is influenced by temperature, process and voltage changes is solved.)

1. A self-calibrating, high precision digital-to-time conversion circuit, comprising:

the digital-to-analog converter comprises a digital-to-analog converter DAC, a capacitor array, a switch array consisting of a plurality of switches and an inverter;

the digital-to-analog converter DAC is connected with the capacitor array; the capacitor array is connected with the phase inverter; the inverter is connected with an output end DTC _ OUT; the digital-to-analog converter DAC, the capacitor array, the phase inverter and the grounding end are respectively provided with a switch;

the capacitor array comprises a fixed capacitor cap and a variable capacitor cap _ vary; the digital-to-analog converter DAC charges the capacitor array according to an input digital control word representing time delay, and feeds back the current change of a reference current source to the variable capacitor cap _ vary, so that compensation calibration is carried out on the capacitance value of the capacitor array; and the phase inverter outputs a clock signal according to the capacitance value of the capacitor array after compensation calibration.

2. The self-calibrating high precision digital-to-time conversion circuit of claim 1, wherein said digital-to-analog converter DAC is a current-mode digital-to-analog converter based on a current-steering architecture, consisting of a reference current source, multiple current mirror branches, and multiple DAC control switches;

and the DAC control switch controls the on-off of the current mirror branch circuit to adjust the current output with different sizes.

3. The self-calibrating, high precision digital-to-time conversion circuit of claim 2, further comprising: a first resistor R1; the variable capacitor cap _ vary is a voltage-controlled capacitor;

one end of the first resistor R1 is connected to a reference current source of the digital-to-analog converter DAC, and the other end is connected to the variable capacitor cap _ vary; and the change of the reference current is sampled in real time through the first resistor R1, the change of the reference current is reflected on the voltage change of the first resistor R1, and the change of the capacitance value of the variable capacitor cap _ vary is controlled so as to perform compensation calibration on the capacitance value of the capacitor array.

4. The self-calibrating, high precision digital-to-time conversion circuit of claim 2, further comprising: a second resistor R2 and an analog-digital conversion circuit ADC;

the variable capacitor cap _ vary comprises a plurality of variable capacitor switches and a fixed capacitance value capacitor controlled by the variable capacitor switches;

one end of the second resistor R2 is connected to a reference current source of the digital-to-analog converter DAC, the other end of the second resistor R2 is connected to the analog-to-digital conversion circuit ADC, and the other end of the analog-to-digital conversion circuit ADC is connected to the variable capacitor cap _ vary; and sampling the change of the reference current in real time through a second resistor R2, reflecting the change of the reference current as the change of the voltage value at two ends of the second resistor R2, further reflecting the change of the output digital control word of the analog-digital conversion circuit ADC, and controlling the variable capacitance switch to perform compensation calibration on the capacitance value of the capacitor array.

5. The self-calibrating, high precision digital-to-time conversion circuit of claim 2, further comprising: an SPI interface;

the variable capacitor cap _ vary comprises a plurality of variable capacitor switches and a fixed capacitance value capacitor controlled by the variable capacitor switches;

the SPI interface is connected with the variable capacitor cap _ vary, and the other end of the SPI interface is connected with an external control terminal through a data line; and inputting a control signal to the SPI through the external control terminal to control the number of the variable capacitance switches to be turned on so as to compensate and calibrate the capacitance value of the capacitor array.

6. The self-calibrating, high precision digital-to-time conversion circuit of claim 1, wherein the capacitance value of said fixed capacitor cap is greater than the capacitance value of said variable capacitor cap _ vary.

7. Self-calibrating high precision digital-to-time conversion circuit according to claims 2-5, characterized in that the transistors of the current mirror branch have a ratio of width to length of 2 in sequence⁰、2¹、2²、2³、……、2ⁿ。

Technical Field

The invention relates to a digital time conversion circuit technology, in particular to a self-calibration high-precision digital time conversion circuit, and belongs to the technical field of digital-analog hybrid integrated circuits.

Background

In recent years, with the development of technology, Phase Locked Loops (PLLs) are widely used in communication, AI, internet of things, sensors, and other applications, and generate a basic clock signal for circuits such as a radio frequency transceiver and a timing control circuit. It has a crucial influence on the performance of the circuit, such as noise.

The phase-locked loop can be classified into an analog charge pump phase-locked loop (CPPLL) and an all-digital phase-locked loop (ADPLL) according to the type of the phase-locked loop. The analog charge pump phase-locked loop has good phase noise performance, but the design complexity and the power consumption are higher than those of an all-digital phase-locked loop, and the all-digital phase-locked loop has the characteristics of low design complexity, easiness in process migration, low power consumption and the like compared with the analog charge pump phase-locked loop. The all-digital phase-locked loop gradually becomes the mainstream trend of phase-locked loop circuit design, but the in-band noise performance of the all-digital phase-locked loop is inferior to that of an analog charge pump phase-locked loop due to the influence of quantization noise. The invention aims to reduce quantization noise by improving the precision of a digital time conversion circuit, thereby realizing the design of a high-precision low-noise phase-locked loop circuit.

Time to Digital Converter (DTC) is an important component of the adpll. The performance of the time-to-digital conversion circuit directly affects the accuracy and noise level of the adpll. Two important performance parameters of time-to-digital conversion circuits are resolution and linearity. The resolution of the time-to-digital conversion circuit directly affects the level of quantization noise. If the resolution of the time-to-digital conversion circuit is too low, the quantization noise of the time-to-digital conversion circuit reaches a high level, and the phase noise in the output band of the phase-locked loop is further influenced. Meanwhile, if the resolution of the time-to-digital conversion circuit is too low, the dynamic resolution of the phase comparator in the phase-locked loop circuit is greatly affected. The resolution of the time-to-digital conversion circuit has a crucial impact on the performance metrics of the phase-locked loop.

At present, the architecture adopted by the digital time conversion circuit is based on the structures of an inverter and a switch circuit. The resolution of the phase error comparator mainly depends on the delay of the unit inverter, which is greatly affected by process differences, temperature variations, and voltage variations. For example, in a 180nm process, the minimum resolution is about 2ps, which is far from the resolution requirement of a high-precision phase-locked loop. The digital time conversion circuit aims to solve the problem of resolution of the digital time conversion circuit under the limitation of process conditions. A design method of a high-precision Digital-to-time conversion circuit based on a current-mode Digital-to-Analog conversion circuit (DAC) is provided. However, in the current-mode digital-to-analog converter circuit, the reference current source in the circuit is affected by temperature, process, and voltage changes, and the output reference current changes accordingly. For a high-precision digital-to-time conversion circuit, a small current change can cause an offside offset of an output clock signal of the high-precision digital-to-time conversion circuit. It becomes particularly important to calibrate a high-precision digital-to-time conversion circuit of a current-mode digital-to-analog conversion circuit. Therefore, aiming at the problems, the design method of the high-precision self-calibration digital time conversion circuit facing the all-digital phase-locked loop is provided, and has important engineering significance.

Disclosure of Invention

The invention aims to solve the technical problem that the output clock signal is offside offset due to the change of the output reference current caused by the change of the reference current source in the current type digital-to-analog conversion circuit under the influence of temperature, process and voltage.

In order to achieve the purpose, the invention adopts the technical scheme that:

a self-calibrating, high precision digital-to-time conversion circuit comprising: the digital-to-analog converter comprises a digital-to-analog converter DAC, a capacitor array, a switch array consisting of a plurality of switches and an inverter; the digital-to-analog converter DAC is connected with the capacitor array; the capacitor array is connected with the phase inverter; the inverter is connected with an output end DTC _ OUT; the digital-to-analog converter DAC, the capacitor array, the phase inverter and the grounding end are respectively provided with a switch; the capacitor array comprises a fixed capacitor cap and a variable capacitor cap _ vary; the digital-to-analog converter DAC charges the capacitor array according to an input digital control word representing time delay, and feeds back the current change of a reference current source to the variable capacitor cap _ vary, so that compensation calibration is carried out on the capacitance value of the capacitor array; and the phase inverter outputs a clock signal according to the capacitance value of the capacitor array after compensation calibration.

Furthermore, the digital-to-analog converter DAC is a current type digital-to-analog converter based on a current steering structure and consists of a reference current source, a plurality of current mirror branches and a plurality of DAC control switches; and the DAC control switch controls the on-off of the current mirror branch circuit to adjust the current output with different sizes.

Further, still include: a first resistor R1; the variable capacitor cap _ vary is a voltage-controlled capacitor; one end of the first resistor R1 is connected to a reference current source of the digital-to-analog converter DAC, and the other end is connected to the variable capacitor cap _ vary; and the change of the reference current is sampled in real time through the first resistor R1, the change of the reference current is reflected on the voltage change of the first resistor R1, and the change of the capacitance value of the variable capacitor cap _ vary is controlled so as to perform compensation calibration on the capacitance value of the capacitor array.

Further, still include: a second resistor R2 and an analog-digital conversion circuit ADC; the variable capacitor cap _ vary comprises a plurality of variable capacitor switches and a fixed capacitance value capacitor controlled by the variable capacitor switches; one end of the second resistor R2 is connected to a reference current source of the digital-to-analog converter DAC, the other end of the second resistor R2 is connected to the analog-to-digital conversion circuit ADC, and the other end of the analog-to-digital conversion circuit ADC is connected to the variable capacitor cap _ vary; and sampling the change of the reference current in real time through a second resistor R2, reflecting the change of the reference current as the change of the voltage value at two ends of the second resistor R2, further reflecting the change of the digital control word output by the analog-digital conversion circuit ADC, and controlling the variable capacitance switch to perform compensation calibration on the capacitance value of the capacitor array.

Further, still include: an SPI interface; the variable capacitor cap _ vary comprises a plurality of variable capacitor switches and a fixed capacitance value capacitor controlled by the variable capacitor switches; the SPI interface is connected with the variable capacitor cap _ vary, and the other end of the SPI interface is connected with an external control terminal through a data line; and inputting a control signal to the SPI through the external control terminal to control the number of the variable capacitance switches to be turned on so as to compensate and calibrate the capacitance value of the capacitor array.

Further, the capacitance value of the fixed capacitor cap is larger than that of the variable capacitor cap _ vary.

Further, the ratio of the width to the length of the transistors of the current mirror branch is 2 in sequence⁰、2¹、2²、2³、……、2ⁿ。

Compared with the prior art, the self-calibration high-precision digital time conversion circuit has the following advantages:

1) a high-precision self-calibration digital-to-time conversion circuit based on a current-mode digital-to-analog conversion circuit, wherein the minimum resolution delta t is (C delta U)/I, and the precision of the minimum resolution digital-to-analog conversion circuit is determined. The minimum resolution delta U which can be realized by the high-precision digital-analog conversion circuit can be from dozens of uV to several mV, and the resolution of the digital-time conversion circuit can reach ps magnitude and even fs magnitude.

2) The quantization noise can be reduced to a great extent, and the design of the low-noise phase-locked loop is realized.

3) The self-calibration of the charging voltage of the capacitor plate can be realized, the reliability is better, and the design facing to the low-noise all-digital phase-locked loop is facilitated.

Drawings

FIG. 1 is a block diagram of a self-calibrating high precision digital-to-time conversion circuit of the present invention;

FIG. 2 is a block diagram of a self-calibrated high precision digital-to-time conversion circuit with a first resistor R1;

FIG. 3 is a block diagram of a self-calibrated high-precision digital-to-time conversion circuit based on ADC control of an analog-to-digital conversion circuit;

FIG. 4 is a block diagram of an SPI-based self-calibrating, high-precision digital-to-time conversion circuit that is controllable off-chip.

Detailed Description

The invention is further illustrated by the following examples:

example 1

As shown in fig. 1, the present embodiment discloses a self-calibrated high-precision digital-to-time conversion circuit, which includes: the digital-to-analog converter comprises a digital-to-analog converter DAC, a capacitor array, a switch array and an inverter; the digital-to-analog converter DAC is connected with the capacitor array; the capacitor array is connected with the phase inverter; the inverter is connected with an output end DTC _ OUT; the DAC, the capacitor array, the phase inverter and the grounding end are respectively provided with a switch array; the capacitor array comprises a fixed capacitor cap and a variable capacitor cap _ vary; and the digital-to-analog converter DAC charges the capacitor array according to the input digital control word. The self-calibration technology utilizes feedback to feed back a change signal of a reference current source to a variable capacitance value capacitor cap _ vary, so as to compensate and calibrate the capacitance value of the capacitor array; the inverter outputs a clock signal according to the capacitance value of the capacitor array after calibration and compensation.

The digital-to-analog converter DAC is a current type digital-to-analog converter, outputs charging current and charges a capacitor to a specific voltage; the capacitor array is mainly divided into a variable capacitor array and a fixed capacitance value capacitor array, wherein the capacitance value of the fixed capacitance value array is larger than that of the variable capacitor array. The variable capacitor array can realize the change of the capacitance value under certain control, thereby realizing the self-calibration function; and the switch array realizes the switching of the circuit between different working stages by switching the capacitor charging and discharging loop. Thereby realizing the functions of the circuit normally. By the design, the problems of high precision and self calibration of the digital time converter can be solved, and the precision and the reliability of the digital time converter are improved, so that the precision of the all-digital phase-locked loop is improved, the noise of a PLL is reduced, and the performance of the all-digital phase-locked loop is improved.

Example 2

As shown in fig. 1, the digital-to-analog converter DAC of the present embodiment is a current-mode digital-to-analog converter based on a current-steering structure. The structure of the circuit mainly comprises a reference current source, a plurality of current mirror branches and a control switch. The width-length ratio of the transistors of the current mirror branches is different, and the width-length ratio is 2 according to the designed digit number of the digital-analog converter⁰、2¹、2²、2³、……、2ⁿ. The control switch is controlled by a digital signal, and the current output with different sizes is realized by controlling the on-off of each current mirror branch. Based on the method, the charging current of the capacitor array can be accurately controlled, and along with the improvement of the precision of the digital-analog converter, the precision of the corresponding digital-time conversion circuit is also improved. For example, under the process of 180nm, the precision of the digital time conversion circuit of the digital-to-analog converter based on the precision of 10bit and above can reach fs magnitude, and the precision of the digital time conversion circuit is greatly improved.

The capacitor array is divided into a fixed capacitance value capacitor array and a variable capacitance value capacitor array. The capacitance value of the fixed capacitance value capacitor array is larger than that of the variable capacitance value capacitor array. The current generated by the digital-analog converter charges the capacitor array, and the charging and discharging time is controlled by the switch. Formula of charging by capacitor

It can be seen that the capacitor will be charged to a certain fixed level value under the condition of constant charging current and constant charging time. The capacitance value of variable capacitor array can be changed, through the capacitance value that changes variable capacitor array to change the appearance value by the charging capacitance, make at charging current because factor influences such as voltage, temperature, technology compensate the calibration to the capacitance value by the charging capacitor array when the deviation appears, thereby realize calibrating charging back plate voltage value, the current source can provide constant current for the electric capacity secondary charging.

The switch array is to switch the circuit between different working phases, and the circuit provided in this embodiment has a total of four working phases, which are an initial reset phase, a first charging phase, a second reset phase and a second charging phase. The switching between four different working stages is realized by controlling the on and off of the switch.

The inverter has two functions in the embodiment, the first function is to provide voltage during first reset, the voltage input and output by the inverter is the threshold voltage of the inverter when the inverter is short-circuited end to end, and the threshold voltage of the inverter is determined by the width-length ratio of the PMOS transistor and the NMOS transistor and can be kept constant. This is chosen to provide the initial reset voltage of the capacitor in order to optimize the circuit structure. The second function is to compare the voltage of the right plate of the capacitor with the threshold voltage of the inverter in the second charging stage, and when the voltage of the right plate of the capacitor is higher than the threshold voltage of the inverter, the output of the inverter jumps from low level to high level.

The working flow of the high-precision self-calibration digital time conversion circuit of the all-digital phase-locked loop designed based on the invention is as follows.

First phase (initial reset phase): the first switch S1 is closed, the second switch S2, the third switch S3, and the fourth switch S4 are open. At the moment, the voltage of the left and right polar plates of the capacitor is connected with the output end of the phase inverter, the phase inverter is connected end to end, and the voltage of the left and right polar plates is reset to the threshold voltage of the phase inverter.

Second stage (first charging stage): the second switch S2 is closed and the first switch S1, the third switch S3, and the fourth switch S4 are open. At the moment, the output current I _ DAC of the DAC charges the capacitor array, and the opening time of the second switch S2 is controlled according to the formula

It can be seen that the left plate of the capacitor will be charged to a certain fixed voltage. Because the capacitor has the characteristic of isolating direct current signals, the voltage of the right pole plate of the capacitor keeps the threshold voltage unchanged. Therefore, the left and right plates of the capacitor generate a voltage difference delta V, and the magnitude of the voltage difference is controlled by the input digital signal of the DAC.

In the third phase (second reset phase), the third switch S2 is closed, and the first switch S1, the second switch S3, and the fourth switch S4 are all open. The left plate of the capacitor array is connected to ground and the left plate voltage is reset to ground. Because the voltage at the two ends of the capacitor can not change suddenly, the voltage difference value at the two ends of the capacitor is not changed, the voltage of the left plate of the capacitor is reset to the ground, and the voltage of the right plate is equal to the original voltage difference value delta V at the two ends of the capacitor.

The fourth phase (second charging phase), the fourth switch S2 is closed, and the first switch S1, the second switch S3, and the third switch S4 are all open. At this time, the charging current I _ ref charges the capacitor array, the voltage across the capacitor begins to gradually rise, and the charging slope

Because the voltage values of the left and right polar plates of the capacitor are different and the charging starting voltage value is different, the right polar plate is charged to the threshold voltage of the inverter before or after the left polar plate, and the inverter is triggered to output a high level. By using the clock signal to control the on and off of the fourth switch S4, the delayed clock signal can be obtained at the output end of the inverter, so as to implement the function of the digital-to-time conversion circuit.

Example 3

This embodiment still includes: a first resistor R1; the variable capacitor cap _ vary is a voltage-controlled capacitor; one end of a first resistor R1 is connected with a reference current source of a digital-to-analog converter DAC, and the other end of the first resistor R1 is connected with a variable capacitor cap _ vary; the change of the reference current is sampled in real time through the first resistor R1, and the change of the reference current is reflected on the voltage change of the first resistor R1, so that the change of the capacitance value of the variable capacitor cap _ vary is controlled, and the capacitance value of the capacitor array is calibrated and compensated.

Specifically, as shown in fig. 2, the variable capacitor array is composed of voltage-controlled capacitors. The first resistor R1 has one end connected to a reference current source of the DAC and the other end connected to a voltage-controlled capacitor (cap _ vary). The change of the reference current can be sampled in real time through the first resistor R1, and the change of the reference current is reflected on the voltage change of the first resistor R1, so that the voltage of the voltage-controlled capacitor is controlled to change, the capacitance value of the voltage-controlled capacitor is changed, the capacitance value of the capacitor array is adjusted finally, and the purpose of self calibration is achieved. The specific working flow of the circuit is as follows.

First phase (initial reset phase): the first switch S1 is closed, the second switch S2, the third switch S3, and the fourth switch S4 are open. At the moment, the voltage of the left and right polar plates of the capacitor is connected with the output end of the phase inverter, the phase inverter is connected end to end, and the voltage of the left and right polar plates is reset to the threshold voltage of the phase inverter.

Second stage (first charging stage): the second switch S2 is closed and the first switch S1, the third switch S3, and the fourth switch S4 are open. At the moment, the output current I _ DAC of the DAC charges the capacitor array, and the opening time of the second switch S2 is controlled according to the formula

It can be seen that the left plate of the capacitor will be charged to a certain fixed voltage. Because the capacitor has the characteristic of isolating direct current signals, the voltage of the right pole plate of the capacitor keeps the threshold voltage unchanged. Therefore, the left and right plates of the capacitor generate a voltage difference delta V, and the magnitude of the voltage difference is controlled by the input digital signal of the DAC. In the charging process, the first resistor R1 samples the current change of a reference current source in the DAC, and the current change is converted into a voltage signal to control the voltage-controlled capacitor, so that the capacitance value of the charged capacitor array is changed, the charging voltage is self-calibrated, and the charged voltage value is ensured to be consistent with the input digital control signal.

In the third phase (second reset phase), the third switch S2 is closed, and the first switch S1, the second switch S3, and the fourth switch S4 are all open. The left plate of the capacitor array is connected to ground and the left plate voltage is reset to ground. Because the voltage at the two ends of the capacitor can not change suddenly, the voltage difference value at the two ends of the capacitor is not changed, the voltage of the left plate of the capacitor is reset to the ground, and the voltage of the right plate is equal to the original voltage difference value delta V at the two ends of the capacitor.

The fourth phase (second charging phase), the fourth switch S2 is closed, and the first switch S1, the second switch S3, and the third switch S4 are all open. At this time, the charging current I _ ref charges the capacitor array, the voltage across the capacitor begins to gradually rise, and the charging slope

Because the voltage values of the left and right polar plates of the capacitor are different and the charging starting voltage value is different, the right polar plate is charged to the threshold voltage of the inverter before or after the left polar plate, and the inverter is triggered to output a high level. By using the clock signal to control the on and off of the fourth switch S4, the delayed clock signal can be obtained at the output end of the inverter, so as to implement the function of the digital-to-time conversion circuit.

Example 4

This embodiment still includes: a second resistor R2 and an analog-digital conversion circuit ADC; the variable capacitor cap _ vary comprises a plurality of variable capacitor switches and a fixed capacitance value capacitor controlled by the variable capacitor switches; one end of the second resistor R2 is connected with a reference current source of the digital-to-analog converter DAC, the other end of the second resistor R2 is connected with the analog-to-digital conversion circuit ADC, and the other end of the analog-to-digital conversion circuit ADC is connected with the variable capacitor cap _ vary; the change of the reference current is sampled in real time through the second resistor R2, the change of the reference current is reflected to the change of the voltage value at two ends of the second resistor R2 and further reflected to the change of the analog-digital conversion circuit ADC, and the capacitance value of the capacitor array is calibrated and compensated through the control of the variable capacitor switch.

Specifically, as shown in fig. 3, the variable capacitor cap _ vary is composed of a switch array and a fixed-capacitance capacitor array. The second resistor R2 has one end connected to the reference current source of the DAC and the other end connected to the analog-to-digital conversion circuit ADC. The change of the reference current can be sampled in real time through the second resistor R2, and the change of the reference current is reflected to the change of the voltage values at two ends of the second resistor R2 and further reflected to the change of the ADC output digital control word, so that the control of the number of the switched arrays is realized, the adjustment of the capacitance value of the capacitor array is finally realized, and the aim of self calibration is fulfilled. The specific working flow of the circuit is as follows.

First phase (initial reset phase): the first switch S1 is closed, the second switch S2, the third switch S3, and the fourth switch S4 are open. At the moment, the voltage of the left and right polar plates of the capacitor is connected with the output end of the phase inverter, the phase inverter is connected end to end, and the voltage of the left and right polar plates is reset to the threshold voltage of the phase inverter.

Second stage (first charging stage): the second switch S2 is closed and the first switch S1, the third switch S3, and the fourth switch S4 are open. At the moment, the output current I _ DAC of the DAC charges the capacitor array, and the opening time of the second switch S2 is controlled according to the formula

It can be seen that the left plate of the capacitor will be charged to a certain fixed voltage. Because the capacitor has the characteristic of isolating direct current signals, the voltage of the right pole plate of the capacitor keeps the threshold voltage unchanged. Therefore, the left and right plates of the capacitor generate a voltage difference delta V, and the magnitude of the voltage difference is controlled by the input digital signal of the DAC. In the charging process, the change of the reference current can be sampled in real time through the second resistor R2, the change of the reference current is reflected as the change of the voltage values at two ends of the second resistor R2, and further reflected as the change of the digital control word output by the ADC, so that the control on the number of the switched arrays is realized, the adjustment on the capacitance value of the capacitor array is finally realized, the self-calibration is realized, the charging voltage is self-calibrated, and the condition that the charged voltage value is consistent with the input digital control signal is ensured.

In the third phase (second reset phase), the third switch S2 is closed, and the first switch S1, the second switch S3, and the fourth switch S4 are all open. The left plate of the capacitor array is connected to ground and the left plate voltage is reset to ground. Because the voltage at the two ends of the capacitor can not change suddenly, the voltage difference value at the two ends of the capacitor is not changed, the voltage of the left plate of the capacitor is reset to the ground, and the voltage of the right plate is equal to the original voltage difference value delta V at the two ends of the capacitor.

The fourth phase (second charging phase), the fourth switch S2 is closed, and the first switch S1, the second switch S3, and the third switch S4 are all open. At this time, the charging current I _ ref charges the capacitor array, the voltage across the capacitor begins to gradually rise, and the charging slope

Because the voltage values of the left and right polar plates of the capacitor are different and the charging starting voltage value is different, the right polar plate is charged to the threshold voltage of the inverter before or after the left polar plate, and the inverter is triggered to output a high level. By using the clock signal to control the on and off of the fourth switch S4, the delayed clock signal can be obtained at the output end of the inverter, so as to implement the function of the digital-to-time conversion circuit.

Example 5

As shown in fig. 1, the present embodiment further includes: an SPI interface; the variable capacitor cap _ vary comprises a plurality of variable capacitor switches and a fixed capacitance value capacitor controlled by the variable capacitor switches; the SPI interface is connected with a variable capacitor cap _ vary, and the other end of the SPI interface is connected with an external control terminal through a data line; and a control signal is input to the SPI through an external control terminal to control the number of the variable capacitance switches to be opened so as to calibrate and compensate the capacitance value of the capacitor array.

Specifically, as shown in fig. 4, the variable capacitor array is composed of a switch array and a fixed-capacitance capacitor array. One end of the SPI is connected to the outside of the chip through the PAD, and the other end of the SPI is connected with the switch array. Can give SPI through off-chip input control signal, open the control of number through SPI realization to the switch array, finally realize the adjustment to capacitor array capacitance value, realize the purpose of calibration. The specific working flow of the circuit is as follows.

And finally, the capacitance value of the capacitor array is adjusted, and the purpose of self calibration is realized. The specific working flow of the circuit is as follows.

First phase (initial reset phase): the first switch S1 is closed, the second switch S2, the third switch S3, and the fourth switch S4 are open. At the moment, the voltage of the left and right polar plates of the capacitor is connected with the output end of the phase inverter, the phase inverter is connected end to end, and the voltage of the left and right polar plates is reset to the threshold voltage of the phase inverter.

Second stage (first charging stage): the second switch S2 is closed and the first switch S1, the third switch S3, and the fourth switch S4 are open. At the moment, the output current I _ DAC of the DAC charges the capacitor array, and the opening time of the second switch S2 is controlled according to the formula

It can be seen that the left plate of the capacitor will be charged to a certain fixed voltage. Because the capacitor has the characteristic of isolating direct current signals, the voltage of the right pole plate of the capacitor keeps the threshold voltage unchanged. Therefore, the left and right plates of the capacitor generate a voltage difference delta V, and the magnitude of the voltage difference is controlled by the input digital signal of the DAC. In the charging process, can give SPI through off-chip input control signal, realize opening the control of number through SPI to the switch array, finally realize the adjustment to capacitor array capacitance value, calibrate charging voltage, guarantee that the voltage value that charges keeps unanimous with the digital control signal who inputs.

In the third phase (second reset phase), the third switch S2 is closed, and the first switch S1, the second switch S3, and the fourth switch S4 are all open. The left plate of the capacitor array is connected to ground and the left plate voltage is reset to ground. Because the voltage at the two ends of the capacitor can not change suddenly, the voltage difference value at the two ends of the capacitor is not changed, the voltage of the left plate of the capacitor is reset to the ground, and the voltage of the right plate is equal to the original voltage difference value delta V at the two ends of the capacitor.

The fourth phase (second charging phase), the fourth switch S2 is closed, and the first switch S1, the second switch S3, and the third switch S4 are all open. At this time, the charging current I _ ref charges the capacitor array, the voltage across the capacitor begins to gradually rise, and the charging slope

Because the voltage values of the left and right polar plates of the capacitor are different and the charging starting voltage value is different, the right polar plate is charged to the threshold voltage of the inverter before or after the left polar plate, and the inverter is triggered to output a high level. By using the clock signal to control the on and off of the fourth switch S4, the delayed clock signal can be obtained at the output end of the inverter, so as to implement the function of the digital-to-time conversion circuit.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.