CN103036517A - Data bit (dB) linear variable gain amplifier - Google Patents

Abstract

The invention discloses a data bit (dB) linear variable gain amplifier. The dB linear variable gain amplifier is formed by a premier variable gain amplifier, a removing direct current offset circuit A, a secondary variable gain amplifier, and a removing direct current offset circuit B which are used for amplifying signals or weakening and removing direct current offset. Control voltage and gain of the amplifiers are enabled to be in an exponential relationship by an index gain control circuit. Each removing direct current offset circuit is formed by a GM-C tan-conductance filter and a common-mode feedback circuit. Input of the premier variable gain amplifier is used as input of the whole circuit. Output of the premier variable gain amplifier is connected with input of the secondary variable gain amplifier. Output of the secondary variable gain amplifier is used as output of the whole circuit. The dB linear variable gain amplifier is improved based on a Gilbert unit, is used in an automatic gain control circuit, and enables the amplifier to have larger broadband and better linear degree.

Description

A kind of dB linear variable gain amplifier

Technical field

The present invention relates to a kind of integrated circuit (IC) design technology and the communications field, relate in particular to a kind of dB linear variable gain amplifier.

Background technology

In wireless communication system, because under the different situations, there is different distances in transmitter from receiver, add the interference of time variation and the outside noise of communication channel, the impact of these factors can cause the at times strong and at other times weak of signal, causes the amplitude range of receiver input signal to alter a great deal (up to tens dB).In order to receive as far as possible reliably signal, receiver is provided with automatic gain control circuit (Automatic Gain Control, AGC) usually, and variable gain amplifier then is the major part of AGC system.

In the audio/video analogue system, the major requirement amplifier has larger bandwidth, large input/output bound, dB linear relationship, low noise, low-power consumption.International and domestic main flow design technology is 0.18 μ m at present, and research emphasis and difficult point major embodiment are: wide bandwidth, high-gain dynamic range and high linearity.Most of designer is difficult to realize high linearity in the scope that realizes wide bandwidth and high-gain, but the realization high linearity then may have been sacrificed bandwidth and gain.

Variable gain amplifier is divided into two kinds of forms of Open loop and closed loop, the designer adopts the closed-loop structure variable gain amplifier usually, mainly contain based on the variable variable gain amplifier of load, based on the variable variable gain amplifier of mutual conductance, based on several forms of source negative feedback variable gain amplifier, the variable gain amplifier of closed-loop structure uses degenerative form, and performance is comparatively stable, the ratio of resistance is depended in its gain, and the linearity is higher.Yet exist simultaneously following some deficiency: the input and output voltage scope is very little, and the bandwidth of amplifier is inadequate, and DC maladjustment is serious.

In order to realize constant AGC loop stability time and wide gain-adjusted, the variable gain amplifier General Requirements in the AGC loop has the exponential gain characteristic.Yet the MOS device that is operated under the saturation region is a kind of square law device, and namely leakage current and grid overdrive voltage are quadratic relationship.Although be operated in the indicial response that MOS device under the sub-threshold region has intrinsic, because the performances such as the operating frequency of device, noise are subject to serious deterioration under this zone, in radio frequency integrated circuit, generally do not consider the MOS device is biased in this working region.

Summary of the invention

For above-mentioned prior art, the invention provides a kind of dB linear variable gain amplifier, be to improve and get on the basis of Gilbert unit, be applied in the automatic gain control circuit, can make amplifier that larger bandwidth is arranged, better the linearity.

In order to solve the problems of the technologies described above, a kind of dB linear variable gain of the present invention amplifier is by first order variable gain amplifier and disappear DC maladjustment circuit A, second level variable gain amplifier and disappear DC maladjustment circuit B and Exponential gain control the electric circuit constitute; Described first order variable gain amplifier and the DC maladjustment circuit A that disappears are in order to amplify signal or to decay and eliminate DC maladjustment; Described second level variable gain amplifier and the DC maladjustment circuit B that disappears amplify or decay and elimination DC maladjustment in order to signal is carried out the second level; Described Exponential gain control circuit makes the gain of control voltage and amplifier be exponential relationship; The described DC maladjustment circuit that disappears is by G _M-C transconductance filter and a common mode feedback circuit form; The input of first order variable gain amplifier is the signal input part of circuit as a whole, and the output of first order variable gain amplifier connects the input of second level variable gain amplifier, and the output of second level variable gain amplifier is the output of circuit as a whole; The output control terminal of described Exponential gain control circuit connects respectively the gain control end of first order variable gain amplifier and second level variable gain amplifier;

Described first order variable gain amplifier comprises: 5 pipe differential amplifier and common mode feedback circuits of Gilbert unit, subtraction circuit, replacement Gilbert unit tail current; Described Gilbert unit is for signal being amplified or decaying; Described subtraction circuit is used for cooperating G _M-C transconductance filter realizes eliminating the effect of DC maladjustment; The output stage of described Gilbert unit is through described G _MBehind-C the transconductance filter, as the input of subtraction circuit; The 5 pipe differential amplifiers that replace Gilbert unit tail current are output as differential signal, and two difference output ends are controlled respectively the two-way tail current of first order variable gain amplifier, cause two-way electric current inverse change, are used for increasing the amplitude of oscillation of output voltage;

Described Gilbert module gain is expressed as:

A _V=R _D·(I ₁-I ₂) （1）

In the formula (1), A _VThe gain of Gilbert unit, R _DOutput loading, I ₁, I ₂It is respectively the two-way tail current;

Described Gilbert unit adopts the active load network, described active load network is comprised of resistance R 1, capacitor C 1, PMOS pipe MP1, MP2, MP3 and MP4, PMOS pipe MP1 and MP4 have the effect of shunting, size by regulating resistance R1 and capacitor C 1, make the limit extrapolation, and away from zero point, reduce limit to promoting the inhibitory action of bandwidth; In order to increase high-frequency gain, to promote bandwidth.

Being expressed as of described first order variable gain amplifier input/output signal:

$(V_{\mathrm{IN}}-V_{\mathrm{OUT}}\frac{g_m}{\mathrm{sC}})\·A_{V0}=V_{\mathrm{OUT}}---\left(2\right)$

In the formula (2), V _INBe input signal, V _OUTBe output signal, G _MThe mutual conductance of-C transconductance filter adopts the NMOS input to 5 pipe amplifiers of pipe, g _mG _MThe transconductance value of amplifier in the-C transconductance filter; G _MElectric capacity in the-C transconductance filter adopts mos capacitance, 1/ _SC is the equivalent capacitive reactance of transconductance filter; A _V0Be the gain of Gilbert unit, therefore, the gain expressions of variable gain amplifier is:

$A_V=\frac{V_{\mathrm{OUT}}}{V_{\mathrm{IN}}}=\frac{\mathrm{sC}{A}_{V0}}{g_m{A}_V+\mathrm{sC}}---\left(3\right)$

Be higher than under the 20KHz condition in frequency, in the formula (3), g _mA _V＜＜sC, therefore:

$A_V=\frac{V_{\mathrm{OUT}}}{V_{\mathrm{IN}}}=A_{V0}---\left(4\right)$

Can find out that from formula (4) described first order variable gain amplifier has realized eliminating the effect of DC maladjustment;

Described common mode feedback circuit is in order to suppress common-mode signal;

Second level variable gain amplifier is identical with the DC maladjustment circuit A structure that disappears with first order variable gain amplifier with the DC maladjustment circuit B that disappears.

Compared with prior art, the invention has the beneficial effects as follows:

Because variable gain amplifier of the present invention is formed in parallel by two identical Gilbert unit, the input of a Gilbert unit is as the input of variable gain amplifier, output is as the output of variable gain amplifier, and the input of another Gilbert unit (also being subtraction circuit) and output stage are through a G _MLink to each other behind-C transconductance filter the circuit, and gm * Av under high frequency condition " sC, equivalent gain equals the Gilbert module gain, and it is very little to gain under the low frequency condition, so realize eliminating the effect of DC maladjustment.

The Gilbert unit adopts the active load network, under the high-frequency signal, can improve the impedance of whole active load.By the size of regulating resistance and electric capacity, can produce a zero point at suitable frequency place, have the effect that increases high-frequency gain, promotes bandwidth.

Described Exponential gain control module comprises the pseudoindex control relation that makes up according to current squaring rule relation, produce different two-way current squaring relations by control voltage, become the voltage-to-current relation by the current squaring relationship conversion, finally realizing the double-voltage control relation.

By improved variable gain amplifier, eliminated the interference of DC maladjustment, it is obviously linear that the Exponential gain control circuit makes the dB of amplifier gain simultaneously, be applied to guarantee in the automatic gain control circuit stability of cyclic system, even the amplitude of input signal differs greatly, the settling time of system is constant.

Description of drawings

The integrated stand composition of dB linear variable gain amplifier among Fig. 1 the present invention;

Variable gain amplifier principle schematic among Fig. 2 the present invention;

Fig. 3 DCOC DC maladjustment circuit working schematic diagram that disappears;

Fig. 4 DCOC disappear DC maladjustment circuit and common-mode feedback part schematic diagram;

The frequency response characteristic figure of Fig. 5 dB linear variable gain of the present invention amplifier;

Realize dB relation curve between the control signal change in gain among Fig. 6 the present invention.

Embodiment

Below in conjunction with embodiment the present invention is described in further detail.

As shown in Figure 1, a kind of dB linear variable gain of the present invention amplifier, its overall structure is by first order variable gain amplifier and disappear DC maladjustment circuit A, second level variable gain amplifier and disappear DC maladjustment circuit B and Exponential gain control the electric circuit constitute.

Described first order variable gain amplifier and the DC maladjustment circuit A that disappears are in order to amplify signal or to decay and eliminate DC maladjustment; Described second level variable gain amplifier and the DC maladjustment circuit B that disappears amplify or decay and elimination DC maladjustment in order to signal is carried out the second level; Described Exponential gain control circuit makes the gain of control voltage and amplifier be exponential relationship, and namely the dB linear relationship has nothing to do the settling time of amplifier and the amplitude of input signal.

Second level variable gain amplifier is identical with the DC maladjustment circuit A structure that disappears with first order variable gain amplifier with the DC maladjustment circuit B that disappears.The below take first order variable gain amplifier and disappear DC maladjustment circuit A structure as example describes in detail technical scheme of the present invention.

The described DC maladjustment circuit A that disappears is by G _M-C transconductance filter and a common mode feedback circuit form.

The input of first order variable gain amplifier is the signal input part of circuit as a whole, and the output of first order variable gain amplifier connects the input of second level variable gain amplifier, and the output of second level variable gain amplifier is the output of circuit as a whole; The output control terminal of described Exponential gain control circuit connects respectively the gain control end of first order variable gain amplifier and second level variable gain amplifier.

Described first order variable gain amplifier comprises: 5 pipe differential amplifier and common mode feedback circuits of Gilbert unit, subtraction circuit, replacement Gilbert unit tail current; Described Gilbert unit is for signal being amplified or decaying; Described subtraction circuit is used for cooperating G _M-C transconductance filter realizes eliminating the effect of DC maladjustment; The output stage of described Gilbert unit is through described G _MBehind-C the transconductance filter, as the input of subtraction circuit; The 5 pipe differential amplifiers that replace Gilbert unit tail current are output as differential signal, and two difference output ends are controlled respectively the two-way tail current of first order variable gain amplifier, cause two-way electric current inverse change, are used for increasing the amplitude of oscillation of output voltage; Described Gilbert module gain is expressed as:

A _V=R _D·(I ₁-I ₂) （1）

In the formula (1), A _VThe gain of Gilbert unit, R _DOutput loading, I ₁, I ₂It is respectively the two-way tail current, because tail current source attrition voltage nargin in the basic Gilbert unit, limit simultaneously the problems such as the amplitude of oscillation of output voltage, the tail current that replaces the Gilbert unit here with 5 basic pipe differential amplifiers, 5 basic pipe differential amplifiers are output as differential signal, two difference output ends are controlled respectively the size of variable gain amplifier two-way tail current, cause two-way electric current inverse change, and are consistent with the action effect of current source.Reduce stacked metal-oxide-semiconductor, be conducive to low-pressure designs, increased the amplitude of oscillation of output voltage.

Described Gilbert unit adopts the active load network, shown in the first half dotted line frame among Fig. 2, described active load network is comprised of resistance R 1, capacitor C 1, PMOS pipe MP1, MP2, MP3 and MP4, PMOS pipe MP1 and MP4 have the effect of shunting, under the high-frequency signal, can improve the impedance of whole active load.By the size of regulating resistance R1 and capacitor C 1, can produce a zero point at suitable frequency place, have the effect that increases high-frequency gain, promotes bandwidth, the mutual conductance of regulating resistance R1 and PMOS pipe, can make the limit extrapolation, and away from zero point, reduce limit to promoting the inhibitory action of bandwidth.

Very little imbalance just may have a huge impact output signal after the amplification through the two-stage variable gain amplifier, eliminate DC maladjustment by CDS, Chopper and auto zero several method generally speaking, here the improvement by the Gilbert unit, a Gilbert unit with output stage through a G _MBehind-C the circuit, as the input of another Gilbert unit (subtraction circuit), its schematic diagram as shown in Figure 3, being expressed as of described first order variable gain amplifier input/output signal:

$(V_{\mathrm{IN}}-V_{\mathrm{OUT}}\frac{g_m}{\mathrm{sC}})\·A_{V0}=V_{\mathrm{OUT}}---\left(2\right)$

In the formula (2), V _INBe input signal, V _OUTBe output signal, G _MThe mutual conductance of-C transconductance filter adopts the NMOS input to 5 pipe amplifiers of pipe, g _mG _MThe transconductance value of amplifier in the-C transconductance filter; G _MElectric capacity in the-C transconductance filter adopts mos capacitance, saves the area of chip, 1/ _SC is the equivalent capacitive reactance of transconductance filter; A _V0Be the gain of Gilbert unit, therefore, the gain expressions of variable gain amplifier is:

$A_V=\frac{V_{\mathrm{OUT}}}{V_{\mathrm{IN}}}=\frac{\mathrm{sC}{A}_{V0}}{g_m{A}_V+\mathrm{sC}}---\left(3\right)$

Be higher than under the 20KHz condition in frequency, in the formula (3), g _mA _V＜＜sC, equivalent gain equals the Gilbert module gain, and it is very little to gain under the low frequency condition, so realize eliminating the effect of DC maladjustment.Fig. 5 is the frequency response characteristic figure of dB linear variable gain amplifier, can find out the low frequency signal that has disappeared the DC maladjustment circuit for eliminating below the 20KHz.

Therefore:

$A_V=\frac{V_{\mathrm{OUT}}}{V_{\mathrm{IN}}}=A_{V0}---\left(4\right)$

Can find out that from formula (4) described first order variable gain amplifier has realized eliminating the effect of DC maladjustment.

Described common mode feedback circuit shown in the dotted line frame among Fig. 4, is worked as G in order to suppress common-mode signal _MWhen the output voltage V FB+ of-C transconductance filter, VFB-increase, electric current among NMOS pipe MN1, the MN4 increases, the electric current that flows through PMOS pipe MP1 path increases, therefore, the electric current that mirror image flows through PMOS pipe MP2 path increases, because the size of current among NMOS pipe MN8, the MN9 is constant, so the electric current among NMOS pipe MN2, the MN3 reduces, so electric current by node capacitance to amplifier load PMOS charging (grid of MP3, MP4), raise grid voltage, and then reduce VFB+, VFB-output voltage, vice versa.

Described Exponential gain control circuit comprises the pseudoindex control relation that makes up according to current squaring rule relation, produce different two-way current squaring relations by control voltage, become the voltage-to-current relation by the current squaring relationship conversion, finally realizing the double-voltage control relation.

The voltage signal that the Exponential gain control circuit produces is as the input of difference tail current amplifier, the tail current amplifier adopts five basic pipe differential amplifiers, reduce power consumption, the two-way tail current of the output control Gilbert unit of amplifier, the gain of control amplifier obtains the signal that amplifies and dwindle under the frequency range that we want.That shown in Figure 6 is the control signal of dB linear variable gain amplifier and the dB value Relations Among figure of gain, can find out that dB linear variable gain amplifier realized good dB linear relationship, and obtain the gain ranging of 70dB.

Although top invention has been described in conjunction with figure; but the present invention is not limited to above-mentioned embodiment; above-mentioned embodiment only is schematic; rather than restrictive; those of ordinary skill in the art is under enlightenment of the present invention; in the situation that does not break away from aim of the present invention, can also make a lot of distortion, these all belong within the protection of the present invention.

Claims (1)

1. dB linear variable gain amplifier is by first order variable gain amplifier and disappear DC maladjustment circuit A, second level variable gain amplifier and disappear DC maladjustment circuit B and Exponential gain control the electric circuit constitute; It is characterized in that:

Described first order variable gain amplifier and the DC maladjustment circuit A that disappears are in order to amplify signal or to decay and eliminate DC maladjustment;

Described second level variable gain amplifier and the DC maladjustment circuit B that disappears amplify or decay and elimination DC maladjustment in order to signal is carried out the second level;

Described Exponential gain control circuit makes the gain of control voltage and amplifier be exponential relationship;

The described DC maladjustment circuit that disappears is by G _M-C transconductance filter and a common mode feedback circuit form;

The input of first order variable gain amplifier is the signal input part of circuit as a whole, and the output of first order variable gain amplifier connects the input of second level variable gain amplifier, and the output of second level variable gain amplifier is the output of circuit as a whole; The output control terminal of described Exponential gain control circuit connects respectively the gain control end of first order variable gain amplifier and second level variable gain amplifier;

Described first order variable gain amplifier comprises: 5 pipe differential amplifier and common mode feedback circuits of Gilbert unit, subtraction circuit, replacement Gilbert unit tail current;

Described Gilbert unit is for signal being amplified or decaying;

Described subtraction circuit is used for cooperating G _M-C transconductance filter realizes eliminating the effect of DC maladjustment;

The output stage of described Gilbert unit is through described G _MBehind-C the transconductance filter, as the input of subtraction circuit;

Be output as differential signal at the 5 pipe differential amplifiers that replace Gilbert unit tail current, two difference output ends are controlled respectively the two-way tail current of first order variable gain amplifier, cause two-way electric current inverse change, are used for increasing the amplitude of oscillation of output voltage;

Described Gilbert module gain is expressed as:

A _V=R _D·(I ₁-I ₂) （1）

In the formula (1), A _VThe gain of Gilbert unit, R _DOutput loading, I ₁, I ₂Respectively the two-way tail current;

Described Gilbert unit adopts the active load network, described active load network is comprised of resistance R 1, capacitor C 1, PMOS pipe MP1, MP2, MP3 and MP4, PMOS pipe MP1 and MP4 have the effect of shunting, by the size of regulating resistance R1 and capacitor C 1, in order to increase high-frequency gain, to promote bandwidth; The mutual conductance of regulating resistance R1 and PMOS pipe makes the limit extrapolation, and away from zero point, reduces limit to promoting the inhibitory action of bandwidth;

Being expressed as of described first order variable gain amplifier input/output signal:

$(V_{\mathrm{IN}}-V_{\mathrm{OUT}}\frac{g_m}{\mathrm{sC}})\·A_{V0}=V_{\mathrm{OUT}}---\left(2\right)$

In the formula (2), V _INBe input signal, V _OUTBe output signal, G _MThe mutual conductance of-C transconductance filter adopts the NMOS input to 5 pipe amplifiers of pipe, g _mG _MThe transconductance value of amplifier in the-C transconductance filter; G _MElectric capacity in the-C transconductance filter adopts mos capacitance, 1/ _SC is the equivalent capacitive reactance of transconductance filter; A _V0Be the gain of Gilbert unit, therefore, the gain expressions of variable gain amplifier is:

$A_V=\frac{V_{\mathrm{OUT}}}{V_{\mathrm{IN}}}=\frac{\mathrm{sC}{A}_{V0}}{g_m{A}_V+\mathrm{sC}}---\left(3\right)$

Be higher than under the 20KHz condition in frequency, in the formula (3), g _mA _V＜＜sC, therefore:

$A_V=\frac{V_{\mathrm{OUT}}}{V_{\mathrm{IN}}}=A_{V0}---\left(4\right)$

Can find out that from formula (4) described first order variable gain amplifier has realized eliminating the effect of DC maladjustment;

Described common mode feedback circuit is in order to suppress common-mode signal;

Second level variable gain amplifier is identical with the DC maladjustment circuit A structure that disappears with first order variable gain amplifier with the DC maladjustment circuit B that disappears.

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