CN103001596A - Gain programmable fully-differential amplifier with output common-mode imbalance correction - Google Patents

Abstract

The invention discloses a gain programmable fully-differential amplifier with output common-mode imbalance correction. The circuit consists of two single-end amplifiers AMP1 and AMP2 and a resistor R0. The gain of a fully-differential amplifier can be changed by adjusting the value of R0, and the output common-mode level can be changed by changing the resistance in an operational amplifier so as to realize a gain programmable fully-differential amplifier with output common-mode imbalance correction.

Description

A kind of fully-differential amplifier of the gain programmable of proofreading and correct with output common mode imbalance

Technical field

The present invention relates generally to the design field of fully-differential amplifier, refers in particular to a kind of fully-differential amplifier of the gain programmable of proofreading and correct with output common mode imbalance.

Background technology

In present analog CMOS integrated circuit design, particularly in the radio frequency signal receiver, owing to need to faint radiofrequency signal be quantized, usually with ADC it is quantized into digital signal, because the excursion of radiofrequency signal is usually larger, in order to reach the best characteristic of ADC, usually the front end at ADC all can increase a programmable gain amplifier, its objective is according to the amplitude of radiofrequency signal and control its gain, so that the input of ADC keeps certain amplitude as far as possible, thus the performance of raising ADC; In order to guarantee that antijamming capability is strong, this variable gain amplifier adopts the fully differential structure usually, yet all there is a problem in Differential OPAMP, i.e. output common mode imbalance.Certainly there is a lot of methods can solve the problem of output common mode imbalance, such as common-mode feedback, but no matter adopt that a kind of mode, Shortcomings all more or less, or precision is inadequate, or very complicated, and the imbalance of Differential OPAMP output common mode can directly have influence on the performance of ADC before the ADC, always is a difficult point so how to solve the output common mode imbalance of Differential OPAMP.

Summary of the invention

The problem to be solved in the present invention just is: for the technical problem that prior art exists, proposes a kind of fully-differential amplifier of the gain programmable with output common mode imbalance correction.

The solution that the present invention proposes is: circuit is by two single-ended amplifier AMP ₁, AMP ₂And resistance R ₀Form, by regulating R ₀Value, can change the gain of fully-differential amplifier, variable resistor changes the output common mode level in the amplifier by changing, thereby realizes a kind of fully-differential amplifier of the gain programmable of proofreading and correct with the output common mode imbalance.

Description of drawings

Fig. 1 is circuit theory schematic diagram of the present invention; Fig. 2 is the simulation result schematic diagram of circuit of the present invention;

Embodiment

Below with reference to accompanying drawing and implementation the present invention is described in further details.

As shown in Figure 1, this circuit is by two single-ended amplifier AMP ₁, AMP ₂And resistance R ₀Form, by regulating R ₀Value, can change the gain of fully-differential amplifier, can change the output common mode level by the resistance that changes in the amplifier, thereby realize a kind of fully-differential amplifier of the gain programmable of proofreading and correct with the output common mode imbalance; The below is explained respectively gain control system and two kinds of patterns of output common mode correction.

◆ gain control

Carry out small-signal analysis according to the circuit structure such as Fig. 1, can release

$\frac{V_{\mathrm{OUT}1}}{V_{\mathrm{IN}1}}=1+2\·\frac{R_1}{R_0}---\left(1\right)$

$\frac{V_{\mathrm{OUT}2}}{V_{\mathrm{IN}2}}=1+2\·\frac{R_4}{R_0}---\left(2\right)$

AMP ₁And AMP ₂Circuit parameter identical, i.e. R ₁=R ₄, institute's two-way change in gain also is identical, changes R ₀, can change the gain of circuit.

◆ output common mode is proofreaied and correct

As shown in Figure 1, in AMP1, suppose that the drain current of PMOS pipe M0 is I ₀, be input and output when equating at balance point, flow through resistance R ₂And resistance R ₃Electric current identical, i.e. I ₀/ 2, because bias voltage VB is constant, M5, M6 are in the saturation region, and its direct current is identical, namely

$I_{M5}=\frac{1}{2}{\mathrm{\μ}}_p{c}_{\mathrm{ox}}{(\mathrm{VDD}-\mathrm{VB}-|V_{\mathrm{THP}}\left|\right)}^2\·[1+{\mathrm{\λ}}_5(\mathrm{VDD}-V_{\mathrm{OUT}1})]---\left(3\right)$

$I_{M6}=\frac{1}{2}{\mathrm{\μ}}_n{c}_{\mathrm{ox}}{(V_{\mathrm{GS}6}-V_{\mathrm{THN}})}^2\·(1+{\mathrm{\λ}}_6{V}_{\mathrm{OUT}1})---\left(4\right)$

Suppose now resistance R ₂Increase r, then NMOS pipe M ₆Grid voltage increases rI ₀/ 2, because the V of M6 _GSIncrease, so I _M6Increase, in order to guarantee I _M5=I _M6, V _OUT1Must reduce, suppose V _OUT1Reduce Δ V, then

${\mathrm{\ΔI}}_{M5}=\frac{1}{2}{\mathrm{\μ}}_p{c}_{\mathrm{ox}}{(\mathrm{VDD}-\mathrm{VB}-|V_{\mathrm{THP}}\left|\right)}^2\·{\mathrm{\λ}}_5\mathrm{\ΔV}---\left(5\right)$

${\mathrm{\ΔI}}_{M6}=\frac{1}{2}{\mathrm{\μ}}_n{c}_{\mathrm{ox}}{(\frac{I_{0}r}{2}+V_{\mathrm{GS}6}-V_{\mathrm{THN}})}^2\·[1+{\mathrm{\λ}}_6(V_{\mathrm{OUT}1}-\mathrm{\ΔV})]-\frac{1}{2}{\mathrm{\μ}}_n{c}_{\mathrm{ox}}{(V_{\mathrm{GS}6}-V_{\mathrm{THN}})}^2\·(1+{\mathrm{\λ}}_6{V}_{\mathrm{OUT}1})---\left(6\right)$

$\mathrm{\ΔV}=\frac{\frac{1}{2}{\mathrm{\μ}}_n{c}_{\mathrm{ox}}{(\frac{I_{0}r}{2}+V_{\mathrm{GS}6}-V_{\mathrm{THN}})}^2\·(1+{\mathrm{\λ}}_6{V}_{\mathrm{OUT}1})-\frac{1}{2}{\mathrm{\μ}}_n{c}_{\mathrm{ox}}{(V_{\mathrm{GS}6}-V_{\mathrm{THN}})}^2\·(1+{\mathrm{\λ}}_6{V}_{\mathrm{OUT}1})}{\frac{1}{2}{\mathrm{\μ}}_n{c}_{\mathrm{ox}}{(\frac{I_{0}r}{2}+V_{\mathrm{GS}6}-V_{\mathrm{THN}})}^2\·{\mathrm{\λ}}_6+\frac{1}{2}{\mathrm{\μ}}_p{c}_{\mathrm{ox}}{(\mathrm{VDD}-\mathrm{VB}-|V_{\mathrm{THP}}\left|\right)}^2\·{\mathrm{\λ}}_5}---\left(7\right)$

As seen the value of Δ V depends on resistance change r and NMOS pipe M ₆Original V _GS6Because the amplifier characteristic, so PMOS pipe M1, M2 grid voltage approximately equal are R ₃Resistance must reduce r, to guarantee both sides DC level balance, so the absolute value of the resistance change of R2 and R3 is identical, but opposite direction, namely one becomes large, one diminishes.Hence one can see that exports OUT ₁DC level can be by changing R ₂And R ₃Resistance regulate, in like manner can regulate AMP ₂Resistance R ₅And R ₆Regulate OUT ₂DC level, and R ₅And R ₆Resistance change also is that absolute value is identical, but opposite direction, namely one becomes large, and one diminishes, and R ₂And R ₅Change identical, R ₃And R ₆Change identical, like this V _OUT1And V _OUT2All changed Δ V, but one is positive change, one is inverse change, the variable quantity of its output common mode voltage

ΔV _CM＝2·ΔV (8)

If supply voltage VDD, bias voltage VB are constant, then Δ V _CMThe positive and negative resistance R that depends on ₂, R ₃, R ₅And R ₆Change direction, the absolute value of its variation depends on resistance R ₂, R ₃, R ₅And R ₆The absolute value that changes is with R as shown in Figure 2 ₂And R ₅Become first and diminish greatly again R ₃And R ₆Change the Simulation results schematic diagram of gained by opposite mode.

In sum, the present invention can realize a kind of fully-differential amplifier of the gain programmable of proofreading and correct with output common mode imbalance, has simple in structurely, and control precision is adjustable, and control mode is advantage flexibly.

Claims (1)

1. the fully-differential amplifier of a gain programmable of proofreading and correct with output common mode imbalance is characterized in that:

By two amplifier AMP ₁, AMP ₂And resistance R ₀Form; AMP ₁By PMOS pipe M ₀, PMOS manages M ₁, PMOS manages M ₂, PMOS manages M ₅, NMOS manages M ₃, NMOS manages M ₄, NMOS manages M ₆, resistance R ₁, resistance R ₂, resistance R ₃And capacitor C ₁Form IN ₁AMP ₁Input port, receive PMOS pipe M ₁Grid, OUT ₁Be output port, receive PMOS pipe M ₅With NMOS pipe M ₆Drain electrode and resistance R ₁, capacitor C ₁An end, resistance R ₁The other end is connected to PMOS pipe M ₂Grid, capacitor C ₁The other end is connected to NMOS pipe M ₆Grid, PMOS manage M ₁Drain electrode and NMOS pipe M ₃Drain electrode, PMOS manages M ₀, PMOS manages M ₅Grid be connected to offset signal VB, their source electrode is connected to power supply, PMOS manages M ₁, PMOS manages M ₂Source electrode and PMOS pipe M ₀Drain electrode link to each other, NMOS manages M ₄The grid leak short circuit, and with NMOS pipe M ₃Grid link to each other to form current-mirror structure, PMOS manages M ₂Drain electrode and NMOS pipe M ₄Drain electrode link to each other variable resistor R ₂, R ₃An end be connected respectively to NMOS pipe M ₃, M ₄Source electrode, other end ground connection, NMOS manages M ₆Source ground; AMP ₂By PMOS pipe M ₇, PMOS manages M ₉, PMOS manages M ₁₀, PMOS manages M ₁₁, NMOS manages M ₁₂, NMOS manages M ₁₃, NMOS manages M ₈, resistance R ₄, resistance R ₅, resistance R ₆And capacitor C ₂Form its connected mode and AMP ₁In full accord, IN ₂Be AMP ₂Input port, OUT ₂Be output port; Resistance R ₀Two ends are connected respectively to AMP ₁Middle PMOS pipe M ₂Grid and AMP ₂Middle PMOS pipe M ₁₀Grid; By regulating R ₀Value, can change the gain of fully-differential amplifier, by regulating the variable resistor R in the amplifier ₂, R ₃, R ₅And R ₆, can proofread and correct the output common mode level, thereby realize a kind of fully-differential amplifier of the gain programmable of proofreading and correct with output common mode imbalance.

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