阅读说明：本技术 一种基于可编程衰减器的宽带程控移相电路 (Broadband program-controlled phase-shifting circuit based on programmable attenuator ) 是由 徐浩航 姜乃卓 樊丹婷 于 2021-05-31 设计创作，主要内容包括：本发明涉及了一种基于可编程衰减器的高稳定性宽带程控移相电路。该系统包括：移相网络,基于可编程衰减器的程控低通滤波器。有益效果：和传统的基于压控增益放大器的程控移相电路相比较,本发明电路具有工作频率带宽大,移相精度高,输出波形噪声小,失真小,电路稳定,不易自激等优点。(The invention relates to a high-stability broadband program-controlled phase-shifting circuit based on a programmable attenuator. The system comprises: phase shift network, programmable low-pass filter based on programmable attenuator. Has the advantages that: compared with the traditional program control phase shift circuit based on the voltage-controlled gain amplifier, the circuit has the advantages of large working frequency bandwidth, high phase shift precision, small output waveform noise, small distortion, stable circuit, difficult self-excitation and the like.)

1. A wideband programmable phase shift circuit comprising:

the phase-shifting network circuit comprises two operational amplifiers which are in phase cascade connection, wherein a primary operational amplifier divides an input signal into two paths, one path enters the non-inverting input end of a second-stage operational amplifier through a controllable low-pass filter, the other path is connected with the inverting input end of the second-stage operational amplifier through a divider resistor, and a first feedback resistor is connected between the output end and the inverting input end of the second-stage operational amplifier;

a controllable low pass filter comprising: the active RC filter is connected with the controllable gain unit through the first inverting amplifier, one path of the output end of the controllable gain unit is connected with the inverting input end of the first inverting amplifier through a second feedback resistor, the controllable gain unit changes the current passing through the second feedback resistor through controlling the gain, and the other path of the output end of the controllable gain unit is connected with the second inverting amplifier.

2. The wideband programmable phase shift circuit of claim 1, wherein the controllable gain unit is formed by cascading a programmable attenuator and a fixed gain amplifier, and the controllable attenuator and the fixed gain amplifier are both in one-stage or two-stage cascade form.

3. The wideband programmable phase shift circuit of claim 2, wherein the active RC filter is a first-order RC filter, and when the RC value of the active RC filter is fixed, the wideband programmable phase shift circuit generates different phase shifts for input signals of different frequencies; when the RC value of the active RC filter is adjustable, the amplification factor A of the controllable gain unit is adjusted, so that the phase shift of the broadband program-controlled phase shift circuit on input signals with different frequencies is the same.

4. The wideband programmable phase shift circuit of claim 2 in which the first stage of the controllable gain element is a programmable attenuator and the second stage is a cascade of fixed gain amplifiers when the input signal amplitude exceeds the maximum amplitude of the input allowed by the controllable gain element for maximum gain; when the voltage of the input signal is less than 50mV, the first stage of the controllable gain unit is a fixed gain amplifier, and the second stage is in a cascade form of a programmable attenuator.

5. The broadband program-controlled phase shifting circuit of claim 1, wherein the voltage dividing resistor has the same resistance as the first feedback resistor.

6. The broadband program-controlled phase shifting circuit of claim 1, wherein a voltage follower is used for impedance transformation at the input of the phase shifting network circuit, so that the input impedance of the phase shifting network circuit is high-impedance.

7. The broadband programmable phase shift circuit of claim 2, wherein the programmable attenuator and the fixed gain amplifier are both 1 or two.

8. The broadband programmable phase shift circuit of claim 1, wherein the programmable attenuator is implemented using a chip PE 4302.

Technical Field

The invention relates to a program-controlled phase shifter system, in particular to a broadband program-controlled phase shifting circuit based on a programmable attenuator.

Background

In the fields of radio frequency communication, analog electronics and the like, the phase shift technology is widely applied all the time. By the phase shift technology, various functions such as quadrature modulation, phased array and the like can be completed.

Many phase shifting applications involve fixed or controllable phase shifting over a range of frequencies, whereas conventional phase shifting networks vary in phase with respect to the movement of different frequency points. It is therefore necessary to dynamically vary the parameters of the phase shifting network during circuit operation to achieve a controllable phase shift.

The low-frequency program-controlled phase shifter can be realized by converting an analog signal into a digital domain for digital phase shifting through ADC (analog to digital converter) sampling and then converting the analog signal into an analog signal through a DAC (digital to analog converter); the digital potentiometer can replace a fixed resistor, and the MCU can control the resistance value of the potentiometer to realize phase shift by an equivalent controllable resistor method. But the former has the disadvantages of slow response speed and low working frequency; the latter has the disadvantages of large noise, low adjustment precision, and extremely small resistance value when the working frequency becomes high, so that the working frequency is difficult to extend to a high frequency band. For low-pass structures included in some phase shifting networks, it is contemplated to use a programmable low-pass filter to achieve a controllable phase shift. A traditional program-controlled low-pass filter generally uses a controllable gain amplifier (VGA) to adjust gain so as to further realize control of cut-off frequency of the filter, but the defects of high cost, large noise, insufficient bandwidth and easy self-excitation of the controllable gain amplifier are found in the actual measurement process of a circuit, and the application of a program-controlled phase shifter circuit in a high-frequency range is limited.

On the other hand, in the currently widely used programmable phase shifter circuit, a voltage-controlled gain amplifier for a gain control unit is widely adopted, for example, a voltage-controlled gain amplifier is constructed by using the chip VCA810, and a gain control range of-40 dB to +40dB can be realized. However, there are some disadvantages when using a voltage controlled gain amplifier: 1) the need to use a DAC to generate the dc control voltage to adjust the gain of the voltage controlled amplifier increases the complexity of the circuit. 2) The input/output dynamic range of such voltage-controlled gain amplifier is not large enough (for example, the maximum swing of the output signal of the VCA810 is generally not more than 3V peak-to-peak value, for example, using the VCA821, the dynamic range of the input signal is limited by the external gain resistor, and is generally not large enough), so the phase adjustment range of the programmable phase shifter circuit during actual measurement does not reach the theoretical calculation value, and the phenomenon of output waveform distortion is easy to occur. 3) The voltage-controlled gain amplifier has certain limitation requirements on ripple and noise of direct-current control voltage, and in the actual test process, the self-oscillation sometimes occurs in a program-controlled phase shifter circuit using the voltage-controlled gain amplifier as a controllable gain unit, and relatively large noise is sometimes generated in an output waveform. 4) The gain control bandwidth or the dynamic range of the input and output signals is small, the gain control bandwidth of the voltage controlled gain amplifier chip VCA810 is about 25MHz, and if the voltage controlled gain amplifier chip VCA821 is used, the bandwidth can exceed 100MHz, but the gain control range is only 40 dB.

Disclosure of Invention

The invention designs a broadband program-controlled phase shift circuit based on a programmable attenuator, the working frequency can be expanded to 10MHz and above from a low frequency band, and accurate 90-degree phase shift (IQ baseband signal orthogonal synthesis commonly used in a communication system) and controlled arbitrary phase shift phase of a single-frequency sine wave are realized in a frequency range of more than ten-fold frequency range (by adjusting RC resistance-capacitance parameters), and the specific technical scheme is as follows:

the broadband program-controlled phase shift circuit comprises:

the phase-shifting network circuit comprises two operational amplifiers which are in phase cascade connection, wherein a primary operational amplifier divides an input signal into two paths, one path enters the non-inverting input end of a second-stage operational amplifier through a controllable low-pass filter, the other path is connected with the inverting input end of the second-stage operational amplifier through a divider resistor, and a first feedback resistor is connected between the output end and the inverting input end of the second-stage operational amplifier;

a controllable low pass filter comprising: the active RC filter is connected with the controllable gain unit through the first inverting amplifier, one path of the output end of the controllable gain unit is connected with the inverting input end of the first inverting amplifier through a second feedback resistor, the controllable gain unit changes the current passing through the second feedback resistor through controlling the gain, and the other path of the output end of the controllable gain unit is connected with the second inverting amplifier.

The broadband program-controlled phase shift circuit is further designed in that the controllable gain unit is formed by cascading a programmable attenuator and a fixed gain amplifier, and the controllable attenuator and the fixed gain amplifier are in a one-stage or two-stage cascading mode.

The broadband program-controlled phase-shifting circuit is further designed in that the active RC filter is a first-order RC filter, and when the RC value of the active RC filter is fixed, the broadband program-controlled phase-shifting circuit generates different phase shifts on input signals with different frequencies; when the RC value of the active RC filter is adjustable, the amplification factor A of the controllable gain unit is adjusted, so that the phase shift of the broadband program-controlled phase shift circuit on input signals with different frequencies is the same.

The broadband program-controlled phase shift circuit is further designed in that when the amplitude of an input signal exceeds the maximum input amplitude allowed by the controllable gain unit reaching the maximum gain, the first stage of the controllable gain unit is a programmable attenuator, and the second stage of the controllable gain unit is a cascade form of fixed gain amplifiers; when the voltage of the input signal is less than 50mV, the first stage of the controllable gain unit is a fixed gain amplifier, and the second stage is in a cascade form of a programmable attenuator.

The broadband program control phase shift circuit is further designed in that the resistance values of the voltage dividing resistor and the first feedback resistor are the same.

The broadband program control phase shift circuit is further designed in that a voltage follower is adopted for impedance transformation when the phase shift network circuit is input, so that the input impedance of the phase shift network circuit is high.

The broadband program-controlled phase shift circuit is further designed in such a way that 1 or two programmable attenuators and two fixed gain amplifiers are provided.

The broadband program-controlled phase shift circuit is further designed in such a way that the programmable attenuator uses a chip PE 4302.

The invention has the advantages that:

the broadband program control phase shift circuit based on the programmable attenuator selects two groups of different fixed RC parameter values for the controllable low-pass filter according to different frequency range of input signals during actual measurement. When the accurate 90-degree phase shift is realized, the working frequency range of the program-controlled phase shift circuit corresponding to the first group of fixed RC parameters is 500Hz to 5 KHz; the working frequency range of the program-controlled phase-shifting circuit corresponding to the second group of fixed RC parameters is 500KHz to 5 MHz; for a fixed RC parameter, the program-controlled phase shift circuit can realize accurate 90-degree phase shift of a single-frequency sine wave in a frequency range of ten-fold frequency range.

Compared with the traditional program control phase shift circuit, the circuit has the advantages of large working frequency bandwidth, high phase shift precision, small output waveform noise, small distortion, stable circuit, difficult self-excitation and the like.

The scheme of using the programmable attenuator and the fixed gain amplifier in cascade connection to replace the voltage-controlled gain amplifier in the invention has the following advantages: 1) the direct current control voltage is generated without using a DAC, the attenuation value of the programmable attenuator can be directly set by the singlechip to realize the gain controllable unit, and the circuit design is simplified. 2) The input and output dynamic range of the programmable attenuator is larger (for example, the programmable attenuator can obtain the input dynamic range of 9V peak-to-peak value by using a PE4302 chip, so that the phase adjustment range of the programmable phase shifter circuit in actual measurement is closer to a theoretical calculated value, and the phenomenon of output waveform distortion is not easy to occur. 3) Because direct current control voltage is not required to be generated, and the programmable attenuator is not used for generating self-excitation of the circuit, the self-excitation phenomenon of the circuit is not found in the actual test process of the program control phase shift circuit using the scheme of the invention; meanwhile, the noise generated when the programmable attenuator attenuates and reduces signals is smaller, so that the noise of the output waveform of the circuit is smaller in the actual measurement process. 4) Taking the programmable attenuator PE4302 as an example, the bandwidth of the input signal may exceed 1GHz, and if other operational amplifiers in the programmable phase shifter circuit all use high-speed broadband operational amplifiers, the operating bandwidth of the programmable phase shifter circuit may be greatly expanded. The highest working frequency of the programmable phase shifter circuit designed by the invention can reach 5MHz (the used operational amplifier type is opa820) when the 90-degree phase shift is realized in actual measurement, and is higher than the bandwidth of the programmable phase shifter circuit formed by the voltage-controlled gain amplifier VCA 810. (the measured working frequency is 5MHz, the phase shift range is 186-195 degrees, only about 10 degrees of variable range, and 90 degrees of phase shift can not be obtained.)

Drawings

FIG. 1 is a schematic circuit diagram of a 0-180 degree hysteretic phase shift network.

Fig. 2 is a schematic diagram of a circuit for a controllable low-pass filter based on a programmable attenuator.

Fig. 3 is a schematic diagram of a simulation circuit of a broadband programmable phase shifter based on a programmable attenuator.

Fig. 4 shows simulation results of the programmable phase shifter (the decibels of the attenuation values are linearly taken from 0 to 64 dB).

FIG. 5 is a schematic diagram of a circuit of a broadband programmable phase shifter based on a programmable attenuator, which is fabricated and measured.

Fig. 6 is a measured waveform diagram of a programmable attenuator based wideband programmable phase shifter circuit (input signal frequency 500KHz, attenuation set to minimum, output signal phase shift approximately 177 deg.).

Fig. 7 is a measured waveform diagram of a programmable attenuator based wideband programmable phase shifter circuit (input signal frequency 500KHz, attenuation set to maximum, output signal phase shift approximately 274 °).

Fig. 8 is a measured waveform diagram of a programmable attenuator based wideband programmable phase shifter circuit (input signal frequency is 5MHz, attenuation value is set to minimum, phase shift value of output signal is about 356 °).

Fig. 9 is a measured waveform diagram of a programmable attenuator based wideband programmable phase shifter circuit (input signal frequency 5MHz, attenuation set to maximum, output signal phase shift approximately 230 °).

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

Referring to fig. 3, the wideband programmable phase shift circuit of this embodiment is mainly composed of a phase shift network circuit and a controllable low pass filter based on a programmable attenuator.

The phase-shifting network circuit adopts a 0-180 DEG lag phase-shifting network, wherein the lag network comprises a first-order low-pass filter, and a circuit schematic diagram is shown in figure 1. In the parameter selection of the hysteresis network, the resistance value R9 and R10 are 330 Ω, and a reserved design of 50 Ω resistance matching is left at the input and output ends.

When the phase-shifting network is input, a voltage follower is used for impedance conversion, so that the input impedance of the whole circuit is high. The input signal is divided into two paths after passing through the primary operational amplifier, one path enters the non-inverting input end of the second-stage operational amplifier through the controllable low-pass filter, the other path is connected to the inverting input end of the second-stage operational amplifier through a divider resistor, a first feedback resistor is connected between the output end and the inverting input end of the second-stage operational amplifier, and the resistance value of the first feedback resistor is the same as that of the input resistor at the inverting input end of the second-stage operational amplifier.

After the input signal passes through the hysteresis network, a certain attenuation and phase shift are generated according to the difference of frequencies. The other signal entering the inverting terminal of the operational amplifier obtains an inverting gain of 1 (the feedback resistor and the inverting input terminal have equal resistance values), and produces a phase shift twice that of the first-order RC delay network. Since the phase shift of the first order RC delay network is 0 to 90 degrees, the theoretical maximum value of the phase shift network can be 180 degrees. The transfer function for the phase shifting network is derived as follows:

first order RC hysteresis network transfer function, as in equation (1):

thus, the transfer function of the phase shifting network can be expressed as:

in the formula (2), R represents the resistance value of the resistor in the phase-shifting network.

Substituting j omega into s to obtain the amplitude-frequency response and the phase-frequency response of the phase shift network, and calculating the modulus of the transfer function to know that the amplitudes of the output signal and the input signal are the same.

|V_out|＝|V_in| (3)

Thus, the phase shifting network can produce phase variations in the range of 0 to 180 °.

In this embodiment, the controllable low-pass filter based on the programmable attenuator is a first-order low-pass filter, which is used as the filter in the aforementioned 0-180 ° phase-shifting network, and the performance of the controllable low-pass filter is equivalent to a common first-order RC passive low-pass filter. For a fixed RC value, the phase shift produced by it for input signals of different frequencies is different. It is therefore necessary to adjust the RC value so that input signals of different frequencies obtain the same phase shift. In this embodiment, the function of the programmable attenuator based controllable low-pass filter is equivalent to automatic control of the RC component.

Referring to fig. 2, the controllable low-pass filter based on the programmable attenuator of the present embodiment is composed of an active RC filter, a controllable gain unit and two inverting amplifiers.

The active RC filter adopts an integral structure with resistance-capacitance feedback. When the gain of the controllable gain unit is 1, the controllable gain unit may be considered to be short-circuited. At the moment, the input of the active RC filter is connected to the inverting terminal of the operational amplifier through a resistor, the homodromous terminal of the operational amplifier is grounded, the inverting terminal of the operational amplifier is connected with the output terminal through a resistor and a capacitor which are connected in parallel to form feedback, and the value of the resistor is the same as that of the inverting input terminal connected resistor. When the frequency of the input signal is lower, the capacitor is equivalent to an open circuit, and the circuit at the moment is equivalent to an inverting amplifier; when the frequency of the input signal is increased, the capacitance impedance is reduced, the amplification factor of the inverting amplifier is reduced, and meanwhile, phase shift is introduced, so that the effect of low-pass filtering is realized.

The controllable gain unit of the embodiment changes the current in the feedback resistor of the inverting input terminal of the operational amplifier by controlling the gain. One end of the feedback resistor is connected to the inverting input end of the operational amplifier, and the unidirectional input end of the operational amplifier is grounded, so that one end of the resistor is equivalent to ground (the voltages of the non-inverting end and the inverting end can be considered to be the same when the operational amplifier is in a feedback state). When the gain of the controllable gain unit is increased, the voltage at two ends of the feedback resistor is linearly adjusted, so that the current passing through the feedback resistor is linearly increased, the speed of charging the capacitor is increased, and the signal of the current input frequency is more capacitiveThe controllable low-pass filter circuit unit is easy to pass through, and meanwhile, the phase shift generated by the signal is reduced, so that the effect of improving the cut-off frequency of the controllable low-pass filter is achieved. On the contrary, when the gain of the controllable gain unit is reduced, the effect of reducing the cut-off frequency of the controllable low-pass filter is also achieved, and therefore the control of the cut-off frequency of the controllable low-pass filter is achieved. Such circuit configuration and parameter design is equivalent to changing the time constant of the resistance capacitance in the transfer function of the low-pass filter. When the input signal amplitude exceeds the controllable gain unit, the maximum gain A is reached_maxWhen the allowed input maximum amplitude is obtained, the first stage of the controllable gain unit is a programmable attenuator, and the second stage of the controllable gain unit is a cascade form of a fixed gain amplifier; when the voltage of the input signal is less than 50mV, the first stage of the controllable gain unit is a fixed gain amplifier, and the second stage is in a cascade form of a programmable attenuator.

The transfer function of the first order low pass filter is represented by equation (5):

in the transfer function expression, the fixed RC time constant is directly divided by the amplification factor a of the controllable gain unit, and the cut-off frequency of the first-order low-pass filter can be expressed as:the larger the gain of the controllable gain unit, the higher the cut-off frequency of the corresponding low-pass filter.

According to the derivation of the principle, the adjustment of the amplification factor a of the controllable gain unit is equivalent to the realization of the automatic control of the RC time constant, so that the control of the cut-off frequency of the first-order low-pass filter is realized, and the program-controlled low-pass filter is realized.

In this embodiment, the controllable gain unit is implemented by using a scheme in which a programmable attenuator and a fixed gain amplifier are cascaded. In currently widely used programmable phase shifter circuits, the controllable gain unit is typically implemented by a voltage controlled gain amplifier, for example, a voltage controlled gain amplifier constructed by using the chip VCA810, which can achieve a gain control range of-40 dB to +40 dB. However, when the voltage-controlled gain amplifier is used, a DAC is required to generate a dc control voltage to adjust the gain of the voltage-controlled amplifier, which increases the complexity of the circuit.

In this embodiment, a scheme of cascade connection of a programmable attenuator and a fixed gain amplifier is used to replace a voltage-controlled gain amplifier, the programmable attenuator uses a chip PE4302, and the attenuator is a high-linearity, 6-bit digital radio frequency step attenuator; the maximum attenuation range is 31.5 dB; the attenuation adjustment precision is 0.5dB, and the working frequency range is from DC to 4000 MHz; the maximum input radio frequency signal power is 24dBm, and when 50 ohm is input, the peak-to-peak value of the input signal can reach 9V maximally. Meanwhile, the serial-parallel data interface is supported to program and control the attenuation amount, and the most common single chip microcomputer can be used for directly controlling the attenuation value of the chip.

As shown in fig. 3, this embodiment provides a simulation circuit diagram of the broadband program-controlled phase shift circuit of the present invention, wherein the values of the resistors R1, R2, R3, and R6 are all 330 Ω, the values of the resistors R4 and R5 are 33 Ω, the value of the capacitor C2 is 470pF, the values of the resistors R9 and R8 are 1K Ω and 100 Ω, and the resistor P1 represents a sliding rheostat. The voltage gain of the single-stage amplifier formed by the operational amplifier U5 can be changed by adjusting the position of the slide rheostat tap during circuit simulation, and the voltage gain is equivalent to the function of the controllable attenuator circuit. The resistor R7 is an isolation resistor at the output end, and can be 0 omega during simulation.

The simulated waveform is shown in fig. 4 below, with the abscissa being the input signal frequency and the ordinate being the phase shift value of the output of the programmable phase shifter circuit relative to the input. As can be seen from the simulated waveform diagram, an accurate 90 ° phase shift can be achieved when the input signal frequency is in the range from 300kHz to 6 MHz.

The actually manufactured and tested broadband programmable phase shifter circuit based on the programmable attenuator is shown in the figure 5, the two-stage programmable attenuator PE4302 is connected in series before the amplifier with the fixed gain of 10 times, the maximum attenuation of a single pole is 31.5dB, the maximum attenuation after cascade connection can reach 63dB, and the adjustment precision of the attenuation is 0.5 dB.

The main circuit parameter settings in fig. 5 are described as follows: the values of the resistors R3 and R4 are 33 omega, the value of the capacitor C1 is 100pF, the values of the resistors R5 and R6 are 9k omega and 1k omega, and the U3 operational amplifier single stage forms an amplifier with fixed 10-time gain.

According to the broadband program-controlled phase shifter based on the programmable attenuator, the working frequency range of the phase shifter capable of realizing accurate 90-degree phase shifting of single-frequency sine waves is 500Hz to 5KHz when the value of the resistor R4 is 3.3K omega and the value of the capacitor C2 is 10nF through actual measurement; when the value of the resistor R4 is 33 omega and the value of the capacitor C2 is 100pF, the working frequency range for realizing accurate 90-degree phase shift is 500KHz to 5 MHz. The program control phase shift circuit can realize precise 90-degree phase shift of a single-frequency sine wave in a frequency range of ten-fold frequency range or controlled phase shift in a range of 0-360 degrees. If 2 PE4302 attenuator chips are cascaded in the controllable gain unit, the total attenuation is 0 to 63dB, the stepping precision is 0.5dB, 128 stepping values are provided in total, and after the controllable gain unit is cascaded with the fixed gain amplifier, 128 different gain values can be realized by the controllable gain unit. Actually, the phase shift precision of the phase shifter is 1 degree on average, the phase shift precision slightly changes according to the difference of phase shift values, preferably about 0.5 degrees (in the center of the phase shift degree range), and at worst, the phase shift precision reaches about 1.5 degrees (at the edge of the phase shift degree range).

Several measured input-output waveforms of a programmable attenuator based wideband programmable phase shifter circuit are shown in fig. 6-9 below. In fig. 6, the input signal has a frequency of 500kHz and an amplitude of 200mVpp, and the attenuation value of the controllable attenuator is set to be minimum, and the amplitude of the obtained output signal is almost constant, and the phase shift value of the output signal is about 177 °. In fig. 7, the parameters of the input signal are unchanged, the attenuation value is set to be maximum, the amplitude of the output signal is almost unchanged, and the phase shift value of the output signal is about 274 °. In fig. 8, the input signal has a frequency of 5MHz and an amplitude of 200mVpp, and the attenuation value of the controllable attenuator is set to be minimum, the amplitude of the output signal is almost constant, and the phase shift value of the output signal is about 356 °. In fig. 9, the parameters of the input signal are unchanged, and when the attenuation value is set to be maximum, the amplitude of the output signal is almost unchanged, and the phase shift value of the output signal is about 230 °.

The foregoing is only a preferred embodiment of this patent and it should be noted that modifications can be made by those skilled in the art without departing from the principle of the invention and these modifications should also be considered as the protection scope of the patent.