CN101924527B - Broadband programmable gain amplifier with precise gain step size - Google Patents
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- CN101924527B CN101924527B CN 201010285999 CN201010285999A CN101924527B CN 101924527 B CN101924527 B CN 101924527B CN 201010285999 CN201010285999 CN 201010285999 CN 201010285999 A CN201010285999 A CN 201010285999A CN 101924527 B CN101924527 B CN 101924527B
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Abstract
The invention belongs to the technical field of integrated circuits, in particular to a broadband programmable gain amplifier with precise gain step size. The broadband programmable gain amplifier comprises a passive attenuation network, an active gain controller and two fixed gain amplifiers. Firstly, a signal passes through the attenuation network, and the corresponding attenuation intensity is selected according to the size of an input signal to acquire a signal with moderate amplitude; the signal is amplified through a first-level fixed gain amplifier to enter the active gain controller to acquire a precise gain; and the signal is amplified through a second-level fixed gain amplifier to acquire a final signal. The active gain controller mainly consists of two connected feedback loops, and the precise gain step size is acquired through controlling the relative intensity of the two feedback loops. The invention can meet the requirements on continuous improvement of VGA gain precision and flat band width in systems, such as communication systems, disc reading systems and the like.
Description
Technical field
The invention belongs to technical field of integrated circuits, be specifically related to a kind of high-precision variable grain amplifier.
Background technology
Read at radio communication, disk, the field such as medicine equipment, analogue system signal to be dealt with has larger dynamic range.For example, code division multiple access (CDMA) communication system needs the change in gain of about 80dB.In order to obtain a signal that amplitude is relatively constant, in similar analogue system, automatic gain of general employing is controlled (AGC) loop, and it correspondingly regulates the gain of link so that output amplitude is constant according to the amplitude size that receives signal.The core of automatic gain control loop is a variable gain amplifier (VGA), automatic gain control loop relatively generates a control signal by output signal and the reference signal with VGA, and the gain of controlling VGA equates the amplitude of its output signal and reference signal.So the gain dynamic range of VGA is larger, gain is better or gain step size is meticulousr with the dB linearity of control signal, and bandwidth is wider, and automatic gain control loop also just has better performance so.
Figure 1 shows that a kind of structure of typical variable gain amplifier.This variable gain amplifier 100 mainly comprises a Gilbert cell 101 and an exponential function generator 102.The output of Gilbert cell determines by the product of two signals, if with one of them as input signal, another one has so just realized the function of gain-variable as gain control signal.Exponential function generator 102 produces one and is the output signal of exponential relationship with input signal, then exports control signal as Gilbert cell with this.So the gain of variable gain amplifier 100 and control signal are the relations of index, namely the relation of dB linearity.Yet mainly with the work that concerns of square law, the relation that wants to produce index can only rely on the approximate function with some indexes to cmos device, as Taylor Expansion and pseudoindex function in analog circuit.These functions only could be preferably near exponential function in certain range of variables, and when range of variables was excessive, the error of approximate function and exponential function can cause the gain of amplifier to depart from the dB linearity.In order to make VGA have larger dynamic range and dB is linear preferably, often adopt the method for multistage VGA cascade, but this is to sacrifice noise, the linearity and power consumption as cost.
Figure 2 shows that a kind of variable gain amplifier based on attenuator structure.This variable gain amplifier 201 comprises a trapezoid resistance network attenuator 202, variable transconductance array 203, trans-impedance amplifier 204 and gain control circuit 205.At first carry out in various degree decay by 202 pairs of signals of attenuator, then the signal that decay obtains is connected respectively to the positive input terminal of each variable transconductance module 206.The output of all variable transconductance modules 206 is connected with the input of trans-impedance amplifier 204, and the voltage that trans-impedance amplifier 204 produces is through feeding back to the negative input end of variable transconductance module 206 after electric resistance partial pressure.Gain control circuit 205 is controlled respectively each variable transconductance module 206, makes its mutual conductance change to maximum from zero.If the leftmost mutual conductance module 206 of conducting only, variable transconductance array 203 and trans-impedance amplifier 204 just are equivalent to a unity gain amplifier so, and output Vout equals to input Vin.If only have 206 conductings of second left mutual conductance module, export so Vout through once decay.When the conducting simultaneously of leftmost two modules, the mutual conductance of first left module is larger with respect to the second left module, and output Vout is more approaching input Vin just.So gain control circuit 205 just can obtain the arbitrary signal of an amplitude in attenuator 202 dynamic ranges by the relative intensity of controlling two adjacent mutual conductance modules in variable transconductance array 203.
This structure is actually two-stage gain-adjusted mechanism, and it is first completed a coarse adjustment with attenuator and obtains several large gain step sizes, then as the border, it is carried out fine tuning take the step-length that obtains.So the scope of Continual Gain Actuator adjusting just is limited in an attenuator step-length, to guarantee less gain error.As long as the increased step of attenuator is abundant, this structure just can realize a comparatively accurate gain control in very large gain variation range.Yet the gain accuracy of this structure depends on gain control circuit 205, only has gain control circuit 205 to satisfy desired functional relation, and the gain that just can obtain the dB linearity is controlled.In addition, variable transconductance module 206 MOS device under the state of shutoff and mutual conductance maximum is in different biasings, and its characteristic also differs greatly.Especially when approaching shutoff, the MOS device is in subthreshold value, does not satisfy typical square law relation.So gain comparatively serious error can occur near attenuator 202 step-length the time.And, only have 206 work of two variable transconductance modules in any moment variable transconductance array 203, a plurality of variable transconductance modules 206 of repetition have been wasted area, have limited bandwidth.
In sum, need a kind of circuit and method to overcome the error that gain occurs when approaching near attenuator 202 step-length, module is carried out multiplexing minimizing chip area, increase bandwidth.If gain can be controlled and make into digital controlly, can also save digital to analog converter, facilitate digital system that it is controlled.
Summary of the invention
The object of the invention is to propose a kind of broadband programmable gain amplifier structure with precise gain step size, with the requirement that in the systems such as satisfied communication, disk read, VGA gain accuracy peace bandwidth is improved constantly.
The broadband programmable gain amplifier with precise gain step size that the present invention proposes is based in CMOS technique the relative error between device less, utilizes the ratio of the parameter between the coupling device to realize that accurate gain controls.Its structure as shown in Figure 3, this programmable gain amplifier (300) mainly comprises a passive network attenuator (301), an active gain controller (303), a prime fixed gain amplifier (302) and a rear class fixed gain amplifier (304); At first signal passes through described passive network attenuator (301), and passive network attenuator (301) is selected corresponding decay intensity according to the size of input signal, signal is carried out initial adjustment, to obtain a signal that amplitude is moderate; Then, be amplified into described active gain controller (303) through described prime fixed gain amplifier (302), active gain controller (303) obtains accurate gain step size based on two connected feedback control loops by the relative intensity of controlling two feedback control loops; Obtain final signal at last, then via described rear class fixed gain amplifier (304).
In the present invention, described passive network attenuator (301), employing be that every grade of signal amplitude decays half, selects different decay shelves by gating switch by one group of R-2R structure of consisting of of the identical resistance of size.Its structure as shown in Figure 4.
In the present invention, described prime fixed gain amplifier (302), employing be that two stage amplifer adds active degenerative structure.Two one-stage amplifiers (501) cascade, feedback circuit (502) produce the centre of corresponding feedback signal to two one-stage amplifier (501) according to output signal.The entire gain of circuit is determined by the ratio of first order amplifier and active degenerative equivalent transconductance, the higher precision of the easy generation of the ratio of circuit parameter.The equivalent resistance of circuit output node and intermediate node is all than not adding the multiple that reduces an one-stage amplifier gain when feeding back.Its structure as shown in Figure 5.
In the present invention, described active gain controller (303) as shown in Figure 6, comprise: a single-stage resistance attenuator (601), two identical variable transconductance modules (602), the capacitor array (604) of the active load of a cascode structure (603) and a regulating frequency response.Single-stage resistance attenuator (601) reduces by half the signal of input on amplitude, obtain the signal of the identical and amplitude Ratio invariableness of two phase places, and the meticulous gain that is used for rear class is controlled.The output of two identical variable transconductance modules (602) connects together and is connected on active load (603), the negative input end of two variable transconductances (602) is linked in the output of active load (603), the positive input terminal of two variable transconductances (602) connects respectively two outputs of single-stage attenuator (601), has finally formed the feedback control loop of two interconnection.Capacitor array (604) one ends connect the output of active gain controller (303), and an end connects the input of active gain controller (303), and this alternating current path has compensated the decay of signal under high frequency, increased bandwidth.
In the present invention, described variable transconductance module (602) as shown in Figure 7, difference by six parallel connections is inputted consisting of, the metal-oxide-semiconductor breadth length ratio of adjacent two differential pairs differs one times, second differential pair metal-oxide-semiconductor breadth length ratio is first two times, and the 6th differential pair metal-oxide-semiconductor breadth length ratio is first three twelvefolds, and the tail current source of each differential pair is independent, whether decide by the conducting of controlling tail current source and open which differential pair, thereby determine the equivalent transconductance of variable transconductance module.
The broadband programmable gain amplifier structure that the present invention proposes has precise gain step size, the requirement that in the system such as can satisfy that communication, disk are read, the peaceful bandwidth of VGA gain accuracy is improved constantly.
Description of drawings
Fig. 1. be a kind of typical structure of the variable gain amplifier of prior art.
Fig. 2. be a kind of variable gain amplifier structure based on attenuator.
Fig. 3. be the broadband programmable gain amplifier structure chart of a kind of precise gain step size provided by the invention.
Fig. 4. be the schematic diagram of attenuator in Fig. 3.
Fig. 5. be the structure chart of prime fixed gain amplifier in Fig. 3.
Fig. 6. be the structure chart of active gain controller in Fig. 3.
Fig. 7. be the schematic diagram of variable transconductance module in Fig. 6.
The frequency response characteristic of Fig. 8 broadband programmable gain amplifier under several gains.
Embodiment
Below in conjunction with accompanying drawing, the present invention is further detailed.
Be illustrated in figure 3 as a kind of broadband programmable gain amplifier (300) structure chart with precise gain step size that the present invention proposes, this circuit comprises: passive network attenuator (301), prime fixed gain amplifier (302), active gain controller (303), rear class fixed gain amplifier (304).
Passive network attenuator (301) as shown in Figure 4 adopts identical resistance to consist of the R-2R network, and its attenuation steps is-6.02dB/step.Then by gating switch, select certain grade of deamplification output.Because rear class is capacitive load, so the conducting resistance of MOS switch can't affect the precision of decay in low frequency, due to the reducing of condensance, larger decay can appear in signal under high frequency.
Signal enters fixed gain amplifier shown in Figure 5 through after the preliminary adjusting of attenuator.Signal is first decayed and amplified is because the gain of fixed gain amplifier is wanted can satisfy amplitude than the amplification demand of small-signal, and also can amplify same multiple for the larger signal of amplitude, makes its amplitude output signal excessive.At this moment just need first through attenuator decay, the signal that the amplitude that obtains is moderate.
Active gain controller as shown in Figure 6 (303) is the key modules that realizes that precise gain is controlled.It first with input signal Vin decay, obtains a phase place identical, the signal Va that amplitude is different.Vin and Va receive the positive input terminal of receiving respectively two variable transconductance modules (602), and the equivalent transconductance that makes them is Gm1, Gm2.Two small-signal currents that Vin and Va produce through variable transconductance module (602) flow into the active load (603) of cascode structure simultaneously, make it be R across resistance.The voltage that small-signal current produces through trans-impedance amplifier is fed back to the negative input end of variable transconductance module (602), has so formed to connect a feedback control loop that is connected.According to structure chart as shown in Figure 6, can obtain following formula:
By following formula as can be known, just can obtain the signal of any Vout of amplitude between Va and Vb by the value that changes Gm2/Gm1.Here it is obtains the principle of different gains by changing two feedback control loop intensity.
Variable transconductance module (602) as shown in Figure 7 is formed in parallel by the differential pair of a series of binary weights, and the tail current of differential pair is also the binary weights relation.According to following formula:
Electric current and breadth length ratio are all the twice relation, and to open the transconductance value that obtains after radical sign be also the twice relation to their product so.Therefore the variable transconductance module that to obtain an equivalent transconductance be binary weights.The minimum mutual conductance of order is the unit mutual conductance, and maximum is exactly 32 times of unit mutual conductances.If their combinations just can be obtained the arbitrary integer times mutual conductance of from 1 to 63 unit.The amplitude of supposing again Va is half of Vin, and the equation according to above-mentioned Vout just can calculate the corresponding Gm ratio of certain Vout amplitude so.Such as, wish the relative Vin decay of Vout 1.2dB, namely Vout equals 0.871Vin, is 46 times of unit mutual conductances as long as establish so Gm1, and Gm2 is 16 times of unit mutual conductances.
Because the adjusting that gains is all that the form that decays realizes, so the amplifier of fixed gain also is absolutely necessary.After the coarse adjustment of signal process passive network attenuator (301) and the fine tuning of active gain controller (303), then export after the amplification of rear class fixed gain amplifier.Be illustrated in figure 8 as broadband programmable gain amplifier (300) frequency response under several gains in 6 ~ 12dB gain ranging.
Claims (2)
1. the broadband programmable gain amplifier structure with precise gain step size, is characterized in that comprising a passive network attenuator (301), an active gain controller (303), a prime fixed gain amplifier (302) and a rear class fixed gain amplifier (304); At first signal passes through described passive network attenuator (301), and passive network attenuator (301) is selected corresponding decay intensity according to the size of input signal, and signal is carried out initial adjustment, obtains a signal that amplitude is moderate; Then, this signal is amplified into described active gain controller (303) through described prime fixed gain amplifier (302), active gain controller (303) obtains accurate gain step size based on two connected feedback control loops by the relative intensity of controlling two feedback control loops; Obtain final signal at last, then via described rear class fixed gain amplifier (304);
Described passive network attenuator (301) adopts the R-2R structure that is made of one group of identical resistance of size, and every grade of signal amplitude decays half, selects different decay shelves by gating switch;
Described prime fixed gain amplifier (302) adopts two stage amplifer to add active degenerative structure; Two one-stage amplifiers (501) cascade, feedback circuit (502) produce the centre of corresponding feedback signal to two one-stage amplifier (501) according to output signal;
Described active gain controller (303) comprising: a single-stage resistance attenuator (601), two identical variable transconductance modules (602), the capacitor array (604) of the active load of a cascode structure (603) and a regulating frequency response; Wherein, described single-stage resistance attenuator (601) reduces by half the signal of input on amplitude, obtains the signal of the identical and amplitude Ratio invariableness of two phase places, and the meticulous gain that is used for rear class is controlled; The output of two identical variable transconductance modules (602) connects together and is connected on active load (603), the negative input end of two variable transconductance modules (602) is linked in the output of active load (603), the positive input terminal of two variable transconductance modules (602) connects respectively two outputs of single-stage resistance attenuator (601), has finally formed the feedback control loop of two interconnection; Capacitor array (604) one ends connect the output of active gain controller (303), and an end connects the input of active gain controller (303).
2. the broadband programmable gain amplifier structure with precise gain step size according to claim 1, it is characterized in that described variable transconductance module (602) by the input of the difference of six parallel connections to consisting of, the metal-oxide-semiconductor breadth length ratio of adjacent two differential pairs differs one times, second differential pair metal-oxide-semiconductor breadth length ratio is first two times, the 6th differential pair metal-oxide-semiconductor breadth length ratio is first three twelvefolds, the tail current source of each differential pair is independent, whether decide by the conducting of controlling tail current source and open which differential pair, thereby determine the equivalent transconductance of variable transconductance module (602).
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Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN102158191A (en) * | 2011-03-28 | 2011-08-17 | 广州润芯信息技术有限公司 | Gain control circuit of radio frequency amplifier |
| CN102857183A (en) * | 2012-09-21 | 2013-01-02 | 复旦大学 | Ultrawide band high-precision variable gain amplifier |
| CN103607177B (en) * | 2013-12-05 | 2016-04-20 | 中国电子科技集团公司第三十八研究所 | A kind of circuit solving gain inconsistency between chip batch |
| CN105048982B (en) * | 2015-08-10 | 2018-09-07 | 西安邮电大学 | Variable gain amplifier in radiofrequency signal transceiver chip |
| CN108206680B (en) * | 2016-12-16 | 2023-09-08 | 江苏海瑞达微电子科技有限公司 | Variable gain amplifier |
| CN107222179A (en) * | 2017-06-15 | 2017-09-29 | 哈尔滨工业大学 | With large gain scope, the linear VGA circuits of high-precision double control voltage dB |
| CN108540102B (en) * | 2018-04-23 | 2021-09-10 | 河北工程大学 | Programmable gain amplifier |
| CN108390653B (en) * | 2018-05-14 | 2023-12-01 | 南京信息工程大学 | Broadband program-controlled gain operational amplifier circuit |
| CN109194298A (en) * | 2018-08-31 | 2019-01-11 | 上海迦美信芯通讯技术有限公司 | Programmable gain amplifier amplifier and navigation neceiver |
| CN108768326A (en) * | 2018-08-31 | 2018-11-06 | 上海迦美信芯通讯技术有限公司 | Fine gain step size controlling amplifier and navigation neceiver |
| CN112564656B (en) * | 2019-09-25 | 2023-05-26 | 天津大学 | Bandwidth-reconfigurable variable gain amplifier suitable for 5G communication system |
| CN113114163B (en) * | 2021-05-28 | 2023-08-18 | 东南大学 | Millimeter wave CMOS digital control attenuator with innovative structure |
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2010
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