阅读说明：本技术 一种具有宽带自适应恒定导通电阻的开关 (Switch with broadband self-adaptive constant on-resistance ) 是由 黄鹤 于 2021-08-19 设计创作，主要内容包括：本发明公开了一种具有宽带自适应恒定导通电阻的开关,包括MOS管、电压跟随器、模拟电压加法器、第一电阻及第二电阻,MOS管的输入端连接输入信号及电压跟随器的输入端；第一电阻的一端连接MOS管衬底,另一端连接电压跟随器的输出端及模拟电压加法器的第一输入端；模拟电压加法器的第二输入端连接固定电压；第二电阻的一端连接MOS管栅极,另一端连接模拟电压加法器的输出端,MOS管输出端输出信号。本发明中电阻与寄生电容组成高通通道,弥补电压跟随器、模拟电压加法器的低通特性,从而在全频段实现导通电阻恒定；还可以有效降低导通电阻,提高导通开关的性能；有效增大关断电阻,提高关断隔离性能。(The invention discloses a switch with a broadband self-adaptive constant on-resistance, which comprises an MOS (metal oxide semiconductor) tube, a voltage follower, an analog voltage adder, a first resistor and a second resistor, wherein the input end of the MOS tube is connected with an input signal and the input end of the voltage follower; one end of the first resistor is connected with the MOS tube substrate, and the other end of the first resistor is connected with the output end of the voltage follower and the first input end of the analog voltage adder; the second input end of the analog voltage adder is connected with a fixed voltage; one end of the second resistor is connected with the grid of the MOS tube, the other end of the second resistor is connected with the output end of the analog voltage adder, and the output end of the MOS tube outputs signals. The resistor and the parasitic capacitor form a high-pass channel to make up the low-pass characteristics of the voltage follower and the analog voltage adder, so that the on-resistance is constant in the full frequency band; the on-resistance can be effectively reduced, and the performance of the on-switch is improved; effectively increase the turn-off resistance and improve the turn-off isolation performance.)

1. A switch with a broadband self-adaptive constant on-resistance is characterized by comprising an MOS (metal oxide semiconductor) tube, a voltage follower, an analog voltage adder, a first resistor and a second resistor; the input end of the MOS tube is connected with the input end of the input signal and voltage follower; one end of the first resistor is connected with the MOS tube substrate, and the other end of the first resistor is connected with the output end of the voltage follower and the first input end of the analog voltage adder; the second input end of the analog voltage adder is connected with a fixed voltage; one end of the second resistor is connected with the grid of the MOS tube, the other end of the second resistor is connected with the output end of the analog voltage adder, and the output end of the MOS tube outputs signals.

2. The switch of claim 1, wherein assuming that the parasitic capacitance between the input terminal of the MOS transistor and the substrate is Cbs and the first resistance is Rb, the dominant pole of the voltage follower should be larger than。

3. The switch of claim 1 or 2, wherein the parasitic capacitance between the input terminal and the gate of the MOS transistor is Cgs, the second resistance is Rg, and the main poles of the voltage follower and the analog voltage adder are both larger than。

4. The switch with the broadband adaptive constant on-resistance according to any one of claims 1 to 3, wherein the input end of the MOS transistor is a source electrode, and the output end of the MOS transistor is a drain electrode; or the input end of the MOS tube is a drain electrode, and the output end of the MOS tube is a source electrode.

5. The switch with the broadband adaptive constant on-resistance according to any one of claims 1 to 3, wherein the MOS transistor is an NMOS transistor; the device also comprises a first switch and a second switch, wherein one end of the first switch is connected with the substrate of the NMOS tube, and the other end of the first switch is connected with the lowest potential; one end of the second switch is connected with the grid electrode of the NMOS tube, and the other end of the second switch is connected with the lowest potential.

6. The switch of claim 5, wherein the first switch and the second switch are closed when the switch is off; when the switch is turned on, the first switch and the second switch are in an off state.

7. The switch with the broadband adaptive constant on-resistance according to any one of claims 1 to 3, wherein the MOS transistor is a PMOS transistor; the transistor also comprises a first switch and a second switch, wherein one end of the first switch is connected with the substrate of the PMOS tube, and the other end of the first switch is connected with the highest potential; one end of the second switch is connected with the grid electrode of the PMOS tube, and the other end of the second switch is connected with the highest potential.

8. The switch of claim 7, wherein the first switch and the second switch are closed when the switch is off; when the switch is turned on, the first switch and the second switch are in an off state.

Technical Field

The invention relates to the field of CMOS integrated circuit design, in particular to a switch with a broadband self-adaptive constant on-resistance.

Background

In the application of broadband signal switching, the on-resistance of the switch is difficult to simultaneously ensure that the low-frequency band signal and the high-frequency band signal are kept constant, so that the on-resistance of the switch influences the transmission quality of the signals. A conventional CMOS switch usually adopts a complementary CMOS structure, and as shown in fig. 1, the switch is composed of a PMOS transistor Mp and an NMOS transistor Mn connected in parallel. When the switch is turned on, the gate Gp of the Mp tube is connected with the lowest potential Vss, the substrate contact Bp is connected with the highest potential Vdd, the gate Gn of the Mn tube is connected with the highest potential Vdd, and the substrate contact Bn is connected with the lowest potential Vss. In the application of low frequency band, neglecting the parasitic capacitance effect of MOS transistor, the schematic diagram of its on-resistance is similar to that shown in FIG. 2, Ron _ Mp is the on-resistance of PMOS transistor, Ron _ Mn is the on-resistance of NMOS transistor, switch on-resistance Ron,

（1）

formula (1) wherein Un, Cox, W, L are constants,

Vgs=Vg-Vin （2）

Vbs=Vb-Vin （3）

vin is the input voltage, Vth is the threshold voltage, and Vth is a function of Vbs, i.e., Vth varies with the variation of Vbs, so it can be derived from equations (1), (2) and (3) that the on-resistance Ron varies with the variation of the input voltage Vin, and the resistance of the complementary CMOS switch in fig. 2 varies with the variation of Vin, which will generate large distortion in many switch applications. When the high-frequency-band MOS transistor is applied, the parasitic capacitance effect of the MOS transistor is not negligible, a larger distortion effect is brought, and adverse effects are generated on a conducting signal.

Disclosure of Invention

The purpose of the invention is as follows: in order to solve the problems that the on-resistance of the traditional CMOS complementary switch is easy to change along with the change of an input signal and the full-band on-resistance cannot be constant, the invention provides a switch with a broadband self-adaptive constant on-resistance.

The technical scheme is as follows: the invention provides a switch with a broadband self-adaptive constant on-resistance, which comprises an MOS (metal oxide semiconductor) tube, a voltage follower, an analog voltage adder, a first resistor and a second resistor, wherein the MOS tube is connected with the voltage follower; the input end of the MOS tube is connected with the input end of the input signal and voltage follower; one end of the first resistor is connected with the MOS tube substrate, and the other end of the first resistor is connected with the output end of the voltage follower and the first input end of the analog voltage adder; the second input end of the analog voltage adder is connected with a fixed voltage; one end of the second resistor is connected with the grid of the MOS tube, the other end of the second resistor is connected with the output end of the analog voltage adder, and the output end of the MOS tube outputs signals.

Further, assuming that a parasitic capacitance between the input end of the MOS transistor and the substrate is Cbs and the first resistance is Rb, the dominant pole of the voltage follower should be larger than。

Further, assuming that the parasitic capacitance between the input end and the gate of the MOS transistor is Cgs, the second resistor is Rg, and the dominant poles of the voltage follower and the analog voltage adder should be larger than。

Furthermore, the input end of the MOS tube is a source electrode, and the output end of the MOS tube is a drain electrode; or the input end of the MOS tube is a drain electrode, and the output end of the MOS tube is a source electrode.

Further, the MOS tube is an NMOS tube; the device also comprises a first switch and a second switch, wherein one end of the first switch is connected with the substrate of the NMOS tube, and the other end of the first switch is connected with the lowest potential; one end of the second switch is connected with the grid electrode of the NMOS tube, and the other end of the second switch is connected with the lowest potential.

Further, when the switch is turned off, the first switch and the second switch are in a closed state; when the switch is turned on, the first switch and the second switch are in an off state.

Furthermore, the MOS tube is a PMOS tube; the transistor also comprises a first switch and a second switch, wherein one end of the first switch is connected with the substrate of the PMOS tube, and the other end of the first switch is connected with the highest potential; one end of the second switch is connected with the grid electrode of the PMOS tube, and the other end of the second switch is connected with the highest potential.

Further, when the switch is turned off, the first switch and the second switch are in a closed state; when the switch is turned on, the first switch and the second switch are in an off state.

Has the advantages that: compared with the prior art, the switch with the broadband self-adaptive constant on-resistance is characterized in that the voltage follower and the adder are added, the voltage is input on the substrate and the grid, the self-adaptive input voltage follows, and the effect that the on-resistance of the switch is constant compared with the prior art is achieved; in order to make up for the defects of low-pass characteristics brought by the voltage follower and the analog voltage adder, resistors are added on a substrate and a grid, and the resistors and parasitic capacitors generate high-pass zero points, so that the low-pass characteristics of the voltage follower and the analog voltage adder are made up, frequency compensation is realized, and the switch has constant on-resistance in the full frequency band. The on-resistance can be effectively reduced, the off-resistance can be increased, and the performance of the on-switch can be improved.

Drawings

FIG. 1 is a circuit schematic of a conventional CMOS complementary switch;

FIG. 2 is a graph of the on-resistance of a conventional CMOS complementary switch as a function of input voltage;

FIG. 3 is a schematic circuit diagram according to a first embodiment;

FIG. 4 is a schematic diagram of the bandwidth characteristics of a multi-pole system;

FIG. 5 is a diagram illustrating frequency compensation results according to the first embodiment;

fig. 6 is a schematic circuit diagram of the second embodiment.

Detailed Description

The invention is further explained below with reference to the figures and the specific embodiments.

The first embodiment is as follows:

as shown in fig. 3, a switch with a wideband adaptive constant on-resistance includes a MOS transistor, a voltage follower, an analog voltage adder, a first resistor Rb, and a second resistor Rg. The MOS transistor may be an NMOS transistor or a PMOS transistor, and in this embodiment, an NMOS transistor is taken as an example, and the source S of the NMOS transistor is taken as an input terminal, and the drain D is taken as an output terminal. The source S of the MOS transistor is connected with an input signal Vin and the input end of a voltage follower, one end of a first resistor Rb is connected with a MOS transistor substrate B, the other end of the first resistor Rb is connected with the output end of the voltage follower and the first input end N1 of an analog voltage adder, the second input end N2 of the analog voltage adder is connected with a fixed voltage Von, one end of a second resistor Rg is connected with a MOS transistor grid G, the other end of the second resistor Rg is connected with the output end of the analog voltage adder, and the drain D of the MOS transistor outputs a signal Vout.

When the switch is turned on, the input signal Vin generates a homodromous voltage following voltage Vb through the voltage follower with the unit gain of 1, and since the bandwidth of the voltage follower is limited and Vb can only follow the input signal within the bandwidth, the embodiment is only suitable for the case that the frequency of the input signal belongs to the bandwidth of the voltage follower, and the explanation below is also based on the condition.

Within the bandwidth, the voltage Vb at the substrate B is approximately a copy of Vin, then:

Vbs=Vb-Vs=Vin-Vin=0 (4)

vb through the analog voltage adder generates Vg = Von + Vin, and Vg can only follow signals within the bandwidth. Then:

Vgs=Vg-Vs=Von+Vin-Vin=Von (5)

therefore, Vgs is a fixed voltage input at the second input terminal of the analog voltage adder, and is a constant; vbs is 0, which is also a constant, i.e., Vth does not vary with Vin. The on-resistance Ron of the MOS transistor is obtained by the following formulas (1), (4) and (5):

（6）

therefore, the on-resistance Ron is also constant within the bandwidth, and therefore does not change with the input signal.

The characteristic that the switch is controlled to be turned on and off by using the different states of the B end of the substrate when the switch is turned on and off is called a substrate control technology, and the voltage of the B end is a copy of Vin, so that the threshold voltage Vth (Vin) when the voltage of the B end is Vin is smaller than the threshold voltage Vth (Vss) when the voltage of the B end is Vss because the voltage of the B end is usually larger than Vss (the lowest potential of a system where the switch is located), and the characteristic that the on-resistance of the switch is reduced can be obtained by the formula (6), so that the performance of the switch is improved.

In addition, because the voltage follower and the analog voltage adder have low-pass characteristics, the effect of constant on-resistance can be achieved only in a bandwidth, and in order to make up for the defect, the first resistor Rb and the second resistor Rg are additionally arranged to form a high-pass channel with a parasitic capacitor, so that the switch has the effect of constant on-resistance in the full frequency band.

The parasitic capacitance between the source electrode and the substrate of the MOS tube is Cbs, the parasitic capacitance between the source electrode and the grid electrode of the MOS tube is Cgs, the parasitic capacitance between the grid electrode and the drain electrode of the MOS tube is Cgd, and the parasitic capacitance between the drain electrode and the substrate of the MOS tube is Cbd.

Since the voltage follower has a low-pass characteristic, it is assumed that the voltage follower is a single-point system, and the pole is as shown by pole 1 in fig. 4, and the pole formed by the first resistor Rb and the parasitic capacitor Cbs to the B end in fig. 3 is pole 2, for multi-point systemsThe system bandwidth of the pole system is approximately equal to the pole with lower frequency, as long as the pole 1 of the voltage follower is larger than the pole 2, Vin passes through the voltage follower to Vb, Vb passes through the resistor Rb and then is connected to the substrate of the MOS transistor, the transmission bandwidth from Rb to the B end is determined by the pole 2, as shown in FIG. 5, the main pole is approximately the low-pass characteristic shown by the curve 1, and(ii) a Vin forms a high-pass characteristic through the MOS parasitic capacitor Cbs and then through the resistor Rb to the B terminal, and as shown in fig. 5, the zero point formed by the high-pass characteristic shown in the curve 2 is approximatelyAnd the pole and the zero point are just offset, so that Vin to the substrate B form an approximate all-pass characteristic, and the frequency characteristic of voltage following is greatly widened.

Therefore, in order to have a constant on-resistance of the switch over the full bandwidth, the dominant pole of the voltage follower should be larger than。

Similarly, the dominant pole of the adopted voltage follower and the analog voltage adder should be larger than that of the adopted voltage follower and the adopted analog voltage adder。

At this time, as is clear from the formula (6), the MOS transistor on-resistance Ron is also constant in the entire bandwidth, and therefore does not change depending on the input signal.

Example two:

although the first embodiment solves the problem that the resistance of the switch is constant when the switch is turned on, when the switch is turned off, the switch-off resistance exists, and therefore the second embodiment adds the first switch S2 and the second switch S1 on the basis of the first embodiment.

Compared with the first embodiment, as shown in fig. 6, the second embodiment further includes a first switch S2 and a second switch S1, where one end of the first switch S2 is connected to the substrate B of the MOS transistor, and the other end is connected to the ground Vss; one end of the second switch S1 is connected to the gate G of the MOS transistor, and the other end is connected to the ground Vss. The other parts are the same as the embodiment.

When the switch with the broadband adaptive constant conduction is turned off, the first switch S2 and the second switch S1 are closed, the grid electrode and the substrate are connected to Vss, and the input signal Vin passes through the parasitic capacitor to the low-resistance path V_SSThe isolation of the high frequency band is increased, and because Vth (Vss) is greater than Vth (vin) when the switch is switched on, the off resistance of the switch is increased by the formula (6), and the isolation of the low frequency end is also increased.