Broadband variable gain amplifier
By controlling the conduction counts of transistors M3 and M4 and designing a wideband variable gain amplifier with zero-pole cancellation, the problems of complex structure, high noise, and small bandwidth in the existing technology are solved, achieving flexible gain adjustment and high-frequency amplification.
Patent Information
- Application Number
- CN202610207044.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-02-12
- Publication Date
- 2026-05-22
Smart Images
Figure CN122073460A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of analog integrated circuit technology and relates to a wideband variable gain amplifier. Background Technology
[0002] Variable gain amplifiers (AGA) are core modules in modern wireless communication, radar, and high-precision data acquisition systems, enabling automatic gain control (AGC). They are electronic amplifiers that dynamically adjust their gain based on the input or control signal. Their core function is to adapt to wide variations in the amplitude of the input signal while maintaining signal quality, preventing signal overload or under-amplification. They are widely used in systems requiring dynamic signal processing. Their gain adjustment range, dB linearity, noise figure, and bandwidth directly determine the dynamic range, sensitivity, and signal integrity of the receiving link.
[0003] For VGAs with cascaded open-loop amplifiers, the gain is controlled by analog voltage, and its gain change is continuous. However, there is a conflict between the gain change range and linearity. A higher gain change range often means worse linearity. When there are too many cascaded amplifiers, it can also cause problems with area, power consumption, and noise.
[0004] For VGAs used in closed loops, the gain is controlled by a digital signal. The relationship between the gain variation range and linearity is not significant. Using a closed-loop amplifier with feedback resistors can often achieve good linearity while ensuring the gain variation range. However, the gain variation of such VGAs is often not linear. The gain can only be adjusted to a certain preset value. Furthermore, such VGAs have a large number of feedback resistors and switches, and their area, power consumption, and noise are often higher than those of VGAs used in open loops.
[0005] When receiving data at the SerDes receiver, the serial signal needs to be compensated and amplified at high frequency because the signal is attenuated at high frequency after passing through the transmission line. In order to prevent the high-frequency part of the signal from attenuating again, a large bandwidth circuit is needed to amplify the signal in the entire frequency band.
[0006] In summary, existing variable gain amplifiers are complex in structure, large in area, and have high noise, and their performance in high-frequency amplification is not good enough. Summary of the Invention
[0007] To solve the aforementioned problems in the prior art, the present invention employs a wideband variable gain amplifier, comprising: transistors M1~M4 and resistor R; the input terminal VIN of the wideband variable gain amplifier is connected to the gate terminals of transistors M1 and M2 and one end of resistor R, respectively; the output terminal VOUT of the wideband variable gain amplifier is connected to the drain terminals of transistors M1 and M2 and the other end of resistor R, respectively; the source terminal of transistor M1 is connected to the drain terminal of transistor M3, the source terminal of transistor M3 is grounded; the source terminal of transistor M2 is connected to the drain terminal of transistor M4, and the source terminal of transistor M4 is connected to a power supply.
[0008] The gate terminal of transistor M3 is connected to the CTRLL control signal, and the gate terminal of transistor M4 is connected to the CTRLH control signal; wherein, the CTRLL control signal and the CTRLH control signal are complementary control signals.
[0009] The CTRL1 control signal controls the number of transistors M3 that are turned on, and the CTRLH control signal controls the number of transistors M4 that are turned on.
[0010] The number of transistors M3 and M4 that are turned on is less than 5.
[0011] Transfer function of a wideband variable gain amplifier :
[0012]
[0013] Where R is the resistance value of resistor R. The total transconductance of transistors M1 and M2, Let be the total gate-drain parasitic capacitance of transistors M1 and M2, and s be the complex frequency of the input signal.
[0014] Transfer function Satisfy the following formula:
[0015]
[0016] in, This is the zero-point expression for the transfer function. This is the pole expression for the transfer function.
[0017] The resistance of resistor R is greater than .
[0018] Beneficial effects:
[0019] 1. This invention utilizes the CTRLL and CTRLH control signals to control the current flow by adjusting the conduction levels of transistors M3 and M4, thereby controlling the gain. The adjustment step size is flexible. When the conduction level increases, the current through transistors M1 and M2 increases, resulting in increased transconductance of transistors M1 and M2, and thus increased gain. 2. This invention uses only four transistors and one resistor to implement a wideband variable gain amplifier. It has a simple structure, is easy to implement, and is applicable to most processes. Furthermore, due to the small number of transistors, transistor noise is low. The larger resistance value of the resistor R results in lower equivalent current noise, leading to lower overall amplifier noise. 3. Traditional amplifiers have limited bandwidth and can only amplify low frequencies. In this invention, because the circuit's transfer function has only one zero and one pole, the zero and pole can be made close together to achieve zero-pole cancellation. Therefore, the remaining poles are contributed by the parasitic capacitances of transistors M3 and M4, resulting in a large amplifier bandwidth capable of simultaneously amplifying both high-frequency and low-frequency components of the signal. Attached Figure Description
[0020] Figure 1 A structural diagram of a wideband variable gain amplifier provided in an embodiment of the present invention;
[0021] Figure 2 This is a simulation diagram of a wideband variable gain amplifier provided for an embodiment of the present invention. Detailed Implementation
[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0023] like Figure 1 As shown, this embodiment of the invention employs a wideband variable gain amplifier, comprising: transistors M1~M4 and resistor R; the input terminal VIN of the wideband variable gain amplifier is connected to the gate terminals of transistors M1 and M2 and one end of resistor R, respectively; the output terminal VOUT of the wideband variable gain amplifier is connected to the drain terminals of transistors M1 and M2 and the other end of resistor R, respectively; the source terminal of transistor M1 is connected to the drain terminal of transistor M3; the source terminal of transistor M3 is grounded; the gate terminal of transistor M3 is connected to the CTRL1 control signal; the source terminal of transistor M2 is connected to the drain terminal of transistor M4; the source terminal of transistor M4 is connected to the power supply; and the gate terminal of transistor M4 is connected to the CTRLH control signal.
[0024] The CTRLL control signal controls the number of transistors M3 that are turned on, and the CTRLH control signal controls the number of transistors M4 that are turned on. The CTRLL control signal and the CTRLH control signal are complementary control signals.
[0025] The CTRLL and CTRHL signals change the current by controlling the conduction levels of transistors M3 and M4. When the conduction levels increase, the current through transistors M1 and M2 increases, leading to a greater transconductance in M1 and M2, and thus a greater gain. The transconductance of transistors M1 and M2 can also be controlled by setting different sizes for transistors M3 and M4, thereby controlling the gain. Larger sizes of transistors M3 and M4 result in greater transconductances for M1 and M2, as shown in the following formula.
[0026]
[0027]
[0028] in, , denoted as transconductances of transistors M1 and M2, respectively, and μ is the electron mobility. It is the capacitance per unit area of gate oxide layer. , The dimensions of transistor M3, , The dimensions of transistor M4, , These represent the currents flowing through transistors M1 and M2, respectively.
[0029] The conduction count of transistors M3 and M4 is less than 5, and the change is not significant after it exceeds 5; the size of transistors M3 and M4 is unlimited and can be changed as needed.
[0030] Transfer function of a wideband variable gain amplifier As in the formula:
[0031]
[0032] Where R is the resistance value of resistor R. The total transconductance of transistors M1 and M2, This is the total gate-drain parasitic capacitance of transistors M1 and M2. , denoted as gate-drain parasitic capacitances of transistors M1 and M2, respectively, and s is the complex frequency of the input signal.
[0033] The transfer function of the circuit in this invention has only one zero and one pole. By designing the circuit to make the zero and pole close together, the zero and pole can be canceled out, thus achieving the transfer function... Satisfy the following formula:
[0034]
[0035] in, This is the zero-point expression for the transfer function. This is the pole expression for the transfer function.
[0036] Through the zero-pole cancellation mentioned above, the remaining poles are contributed by the other parasitic capacitances of transistors M3 and M4. Therefore, the amplifier of this invention has a large bandwidth and can amplify the high-frequency and low-frequency parts of the signal simultaneously. The 3dB bandwidth can reach the cutoff frequency of the transistor.
[0037] This invention implements a wideband variable gain amplifier using only four transistors M1~M4 and one resistor R. It has a simple structure, is easy to implement, and is applicable to most manufacturing processes. Furthermore, due to the small number of transistors, transistor noise is low; and because the resistor R has a relatively large resistance value, the equivalent current noise is low, resulting in low overall amplifier noise. The resistance value of R is greater than... Generally .
[0038] like Figure 2 As shown, to further verify the above advantages of the present invention, a wideband variable gain amplifier circuit proposed in this invention was simulated using a 1.2V power supply voltage under a 65nm CMOS process. Each line in the figure corresponds to the number of transistors M1 and M2 that are turned on. The more transistors that are turned on, the greater the gain. As can be seen from the figure, the gain adjustment range of this simulation experiment is 8-10dB, which can be adjusted according to actual needs. Moreover, the bandwidth can easily reach more than 10GHz, and a trade-off between bandwidth and gain can be made according to actual needs.
[0039] The above-described embodiments further illustrate the purpose, technical solution, and advantages of the present invention. It should be understood that the above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A wideband variable gain amplifier, characterized in that, include: Transistors M1~M4 and resistor R; the input terminal VIN of the wideband variable gain amplifier is connected to the gate terminals of transistors M1 and M2 and one end of resistor R, respectively; the output terminal VOUT of the wideband variable gain amplifier is connected to the drain terminals of transistors M1 and M2 and the other end of resistor R, respectively; the source terminal of transistor M1 is connected to the drain terminal of transistor M3; the source terminal of transistor M3 is grounded; the source terminal of transistor M2 is connected to the drain terminal of transistor M4; the source terminal of transistor M4 is connected to the power supply.
2. A wideband variable gain amplifier according to claim 1, characterized in that, The gate terminal of transistor M3 is connected to the CTRLL control signal, and the gate terminal of transistor M4 is connected to the CTRLH control signal; wherein, the CTRLL control signal and the CTRLH control signal are complementary control signals.
3. A wideband variable gain amplifier according to claim 2, characterized in that, The CTRL1 control signal controls the number of transistors M3 that are turned on; the CTRLH control signal controls the number of transistors M4 that are turned on.
4. A wideband variable gain amplifier according to claim 3, characterized in that, The number of transistors M3 and M4 that are turned on is less than 5.
5. A wideband variable gain amplifier according to claim 1, characterized in that, Transfer function of a wideband variable gain amplifier for: ； Where R is the resistance value of resistor R. The total transconductance of transistors M1 and M2, Let be the total gate-drain parasitic capacitance of transistors M1 and M2, and s be the complex frequency of the input signal.
6. A wideband variable gain amplifier according to claim 5, characterized in that, Transfer function Satisfy the following formula: ； in, This is the zero-point expression for the transfer function. This is the pole expression for the transfer function.
7. A wideband variable gain amplifier according to claim 1, characterized in that, The resistance of resistor R is greater than .