CN108563274B - Linear variable gain circuit structure of continuously adjustable decibel - Google Patents

Linear variable gain circuit structure of continuously adjustable decibel Download PDF

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CN108563274B
CN108563274B CN201810220134.2A CN201810220134A CN108563274B CN 108563274 B CN108563274 B CN 108563274B CN 201810220134 A CN201810220134 A CN 201810220134A CN 108563274 B CN108563274 B CN 108563274B
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CN108563274A (en
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鲁征浩
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Suzhou University
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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
    • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
    • G05F1/10—Regulating voltage or current
    • G05F1/46—Regulating voltage or current wherein the variable actually regulated by the final control device is dc
    • G05F1/56—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices

Abstract

The invention discloses a continuous adjustable decibel linear variable gain circuit structure, which comprises: the amplifier comprises an amplifier core circuit, a common-mode output bias circuit, an exponential proportional current generating circuit and an exponential proportional current bias circuit; the continuously adjustable accurate decibel linear variable gain amplifying structure provided by the invention simply, effectively and accurately realizes a transistor channel current which is exponentially changed along with the linear change of an externally-applied control voltage in a differential amplifying transistor pair with a current rudder structure under the condition of ensuring that the total current is not changed, namely the output common-mode voltage is not changed, and the current determines that the transconductance of the transistor is also exponentially changed along with the linear change of the control voltage, thereby realizing a continuously adjustable variable gain amplifier structure meeting decibel linear gain control.

Description

Linear variable gain circuit structure of continuously adjustable decibel
Technical Field
The invention relates to a gain amplifier, in particular to a novel continuous adjustable decibel linear variable gain circuit structure.
Background
Variable gain amplifier circuits are widely used in communication circuit systems, such as automatic gain control, to improve the dynamic range of the system. Typically, such gain control requires that the circuit gain vary exponentially, i.e., in decibel-Linear (dB-Linear), with changes in the Linear control voltage. That is, the control voltage is linear, while the gain is linear in decibels (exponentially varying). There are two broad categories of methods for implementing this function, one is based on a discrete programmable step-by-step digital gain control mechanism, and the other is a pure analog continuously adjustable gain control mechanism. In many applications, pure analog continuous adjustable decibel linear control is required to avoid glitches in digital gain control.
The first method is to adopt a pseudo-exponential (pseudo-exponential) control circuit structure based on Taylor series approximation, and the structure has the defect that the accuracy of exponential relation between gain and voltage is not high; the second is an accurate decibel linear control circuit, which usually uses a triode as a core and obtains a large-range accurate decibel linear gain control relationship through a series of conversion circuits, and this kind of circuit has a wide application range, but the difficulty lies in the design of the large-range accurate decibel linear gain control circuit, and the structure of the decibel linear control of this kind of circuit is usually very complicated.
Disclosure of Invention
The invention provides a continuously adjustable decibel linear control circuit, and achieves the purpose of simplifying the circuit structure by providing a novel exponential current generation and reproduction structure.
The purpose of the invention is as follows: the circuit structure is simple, and the realized amplifying circuit also has the advantage of controllable constant common-mode output voltage.
In order to achieve the purpose, the invention adopts the following technical scheme:
a continuously adjustable decibel linear variable gain circuit structure comprising: the amplifier comprises an amplifier core circuit, a common-mode output bias circuit, an exponential proportional current generating circuit and an exponential proportional current bias circuit;
the amplifier core circuit is a differential pair current rudder structure and comprises a differential pair M consisting of field effect transistors M1 and M21/M2Differential pair M consisting of field effect transistors M3 and M43/M4A pair of differential load resistors R1/R2And tail current biasing transistor M13Input differential signal is VIN+/VIN-Respectively connect the differential pair M1/M2A differential signal of VOUT+/VOUT-，VOUT+Connecting M2/M4Drain electrode of (V)OUT-Connecting M1/M3Of the differential pair M1/M2Respectively through a resistor R1/R2Two pairs of differential pairs M connected to a high level VDD1/M2、M3/M4Are respectively connected to the transistor M13Drain electrode of, M13The source of (2) is grounded;
the common mode output bias circuit generates a voltage VB1Loaded in M13A gate electrode;
the exponential proportional current generating circuit and the exponential proportional current biasing circuit are sequentially connected, and the generated voltage VB2 is loaded on M3/M4A gate electrode; passing voltage VB1And voltage VB2So that the tail current transistor M13Has a bias current of I0Constantly controllable, simultaneously flowing through M1Channel current I of1And I0And is exponential, so that the gain is linearly changed in decibels.
Preferably, the common-mode output bias circuit comprises a differential pair M consisting of field effect transistors M5 and M65/M6Differential pair M consisting of field effect transistors M7 and M87/M8A pair of differential load resistors R3/R4And tail current biasing transistor M14(ii) a Differential pair M5/M6Grid electrode is connected with external common mode voltage VCM，M7/M8The voltage applied to the gate is derived from a bias voltage V generated by an exponential proportional current bias circuitB2Differential load resistance R3/R4Are shorted together and connected to the positive input of an operational amplifier OP1, and the negative input of OP1 is connected to a common-mode reference voltage VCMThe output end voltage VB1 of OP1 is connected with M14Forming a negative feedback loop.
Preferably, the negative feedback loop formed by the common mode output bias circuit and the amplifier core circuit forces the load resistor R in the common mode output bias circuit3/R4Voltage V at the output terminalX1Is equal to VCMThen V isDD-1/2*I0*R＝VCM，I0Determined by the formula, I0＝2*(VDD-VCM)/R。
Preferably, the exponential-proportion current generation circuit comprises a triode Q1、Q2Composed difference structure triode Q1/Q2A pair of differential resistors R5/R6Tail current transistor M16And an operational amplifier OP 2; the positive input terminal Q of the operational amplifier OP22Output end V of branch load resistor RX3Negative input terminal of M connected to output terminal of applied common mode voltage VCM, OP216A gate electrode, and M16And Q2Forming a negative feedback loop.
Preferably, the exponential proportional current bias circuit comprises a differential pair M consisting of field effect transistors M9 and M109/M10Differential pair M consisting of field effect transistors M11 and M1211/M12A pair of differential resistors R7/R8Tail current transistor M15And an operational amplifier OP3, a differential pair M9/M10Connecting differential resistor pairs R7/R8，M11/M12Directly to a supply voltage; tail current transistor M15Gate loading bias voltage V generated in common mode output bias circuitB1Resistance pair R7/R8Is short-circuited and connected to the negative input of an operational amplifier OP3, and the positive input of OP3 is connected to the voltage V generated by the exponential-proportional current generating circuitY1The output terminal of OP3 generates a bias voltage VB2And loaded into the differential pair M11/M12The gate of (2) constitutes a negative feedback loop.
Preferably, the differential pair M1/M2Differential signal V for gate loadingIN+/VIN-Is also set to V during operationCMDue to the replica bias VB1Relation of (1), M14Gate bias voltage sum M13All gate bias voltages are equal to VB1，M13Tail current of equal to M14Tail current of0I.e. I0＝2*(VDD-VCM) and/R, and VX2＝VX1＝VCM(ii) a Differential pair M1/M2Is set to be I1Differential pair M3/M4Is set to be I2In I1And I2In the distribution relationship of (1), I1At a constant I0The proportion of the total current is M3Bias voltage V of gridB2And (4) determining.
Preferably, the exponential-proportion current generation circuit forms a negative feedback loop such that VX3＝VX2＝VCM，Q2Current I of the branchB2Equal to M in the core circuit of the amplifier1Current of branch, i.e. IB2＝I0/2＝(VDD-VCM) (ii)/R, which is a constantly controllable value; while Q2Voltage V applied to the baseRIs a reference voltage, Q1The voltage loaded on the base is a linear control voltage VC。
Preferably, Q1And Q2Current I of two branchesB1And IB2The following relationship holds:
v in formula (1)TkT/q, k is the Boltzmann constant, q is the electron electric quantity, T is the absolute temperature, i.e. IB1And IB2In an exponential relationship, or IB1And I0Presenting an exponential relationship; i isB1This exponential current is at Q1A voltage V is generated across the resistor R of the branchY1Connected to the positive input terminal of an operational amplifier OP3 of the exponential proportional current bias circuit, and generating a bias voltage V by negative feedbackB2。
Preferably, the exponentially proportional current bias circuit forms a negative feedback loop such that the voltage V isY2And VY1Equal, M9/M10Current I flowing through resistor R in branch1/2 is equal to IB1：
Thus, I1And I0In an exponential relationship, wherein I0Is constant and controllable.
Preferably, the gain expression of the continuously adjustable decibel linear variable gain circuit structure is as follows:
wherein C isoxIs the unit area capacitance of the transistor gate oxide layer,is M1Width to length ratio of transistor, munIs the mobility of electrons, R is the load resistance, VDDIs the supply voltage, VCMFor applying a common-mode voltage, VRFor controlling the reference voltage, VCControl voltage, V, being linearly variedTkT/q, k is Boltzmann constant, q is the electronic quantity, T is the absolute temperature, and the gain of the continuously adjustable decibel linear variable gain circuit structure is dependent on the control voltage VCLinear in decibel.
The invention has the advantages that:
the invention provides a continuously adjustable accurate decibel linear variable gain amplifying structure, which simply, effectively and accurately realizes a transistor channel current which is exponentially changed along with the linear change of an externally-applied control voltage in a differential amplifying transistor pair with a current rudder structure under the condition of ensuring that the total current is not changed, namely the output common-mode voltage is not changed, and the current determines that the transconductance of the transistor is also exponentially changed along with the linear change of the control voltage, thereby realizing a continuously adjustable variable gain amplifier structure meeting decibel linear gain control.
Drawings
The invention is further described with reference to the following figures and examples:
FIG. 1 is a schematic diagram of a continuous adjustable decibel linear variable gain circuit configuration of the present invention;
fig. 2 shows the relationship between gain and control voltage for a linear variable gain circuit in decibels implemented using the parameters of table 1.
Detailed Description
As shown in fig. 1, the present invention includes four parts, an amplifying circuit core part of an upper left corner circuit module 1, a common mode output bias circuit of an upper right corner circuit module 2, an exponential proportional current generating circuit of a lower left corner circuit module 3, and an exponential proportional current bias circuit of a lower right corner circuit module 4. The whole invention will be described in detail based on these four sections.
The input end of the whole circuit is VIN+/VIN-The output is VOUT+/VOUT-With an applied common mode voltage of VCMApplying a reference voltage VRApplying a linear gain control voltage VC. The gain of the amplifier, i.e. the ratio of the output signal to the input signal, is dependent on the control voltage VCIs linearly varied in decibels (exponentially varied).
The amplifier core circuit is a traditional differential pair current steering structure, as shown in the upper left corner of fig. 1, and is composed of two pairs of differential pairs M1/M2，M3/M4A pair of differential load resistors R1/R2(resistance values are all R), and a tail current bias transistor M13Composition of input differential signal VIN+/VIN-Output differential signal as VOUT+/VOUT-Setting tail current transistor M13Has a bias current of I0Outputs a differential signal VOUT+/VOUT-Is controlled by a supply voltage VDDMinus the voltage drop 1/2 xi across the resistor R0R, and the gain of the amplifier is AV＝gm1R, wherein gm1Is a transistor M1So that the gain of the amplifier is a function of VCShows a linear change in decibels (exponential change), it is necessary to make the transistor M such that1Or so that the transconductance of transistor M is exponentially varying1Channel current I of1Is exponentially changed. In this design, we make M by replica biasing technique13Tail current of0Keep constant, and simultaneously, through a smart exponential current replication technology, enable M1Channel current I of1With control of voltage VCExhibits an exponential change. Although the circuit structure of the upper left corner amplifier core circuit is seemingly the traditional current steering differential pair structure, the core of the invention is loaded on M13Voltage V of gridB1And is loaded at M3/M4Voltage V of gridB2The two voltages are respectively generated by a second part common-mode output bias circuit and a third part exponential-proportion current generation and bias circuit and a fourth part exponential-proportion current generation and bias circuit in the invention shown in the figure 1, and are respectively generated by VB1And VB2On the one hand, the output common-mode voltage V of the amplifierX2Equal to an applied common mode bias voltage VCMThis means a flowCurrent I of load resistor of over-amplifier0Constantly controllable, on the other hand, to cause a flow through M1Channel current I of1And the total current I0The gain is in exponential relation, thereby achieving the design purpose that the gain is in linear change in decibels.
Implementation of M13Tail current I0The constant method is as follows, as shown in the common mode output bias circuit at the upper right corner of fig. 1, and two pairs of differential pairs M in the partial circuit5/M6，M7/M8Differential load resistance R3/R4And tail current biasing transistor M14And the upper left circuit 1 amplifier core circuit M in FIG. 11/M2，M3/M4Differential load resistance R1/R2Tail current bias transistor M13Identical, differential pair M in the upper right corner circuit 2 of FIG. 15/M6Grid electrode is connected with external common mode voltage VCM，M7/M8The voltage applied to the gate is derived from the bias voltage V generated by the circuit 4 at the lower right corner of FIG. 1B2The output ends of a pair of differential load resistors in the upper right corner circuit 2 of FIG. 1 are shorted together and connected to the positive input end of an operational amplifier OP1, and the negative input end of OP1 is connected to the common-mode reference voltage VCMThe output of OP1 is terminated by M14Forming a negative feedback loop forcing the load resistor R in the upper right corner circuit 2 of fig. 13/R4Voltage V at the output terminalX1Is equal to VCMThis means that the following formula holds VDD-1/2*I0*R＝VCM，I0Can be determined by the formula I0＝2*(VDD-VCM) and/R. Differential input pair M in the upper left corner circuit 1 of FIG. 11/M2Differential signal V for gate loadingIN+/VINThe common-mode voltage is also set to V during operationCMDue to the replica bias VB1In relation (2), that is, the circuit 1 and the circuit 2 in FIG. 1 have the same main structure, M14Gate bias voltage sum M13All gate bias voltages are equal to VB1The current distribution in the top left corner circuit 1 of fig. 1 is identical to the top right corner circuit 2, i.e. M13Tail power ofFlow equals M14Tail current of0I.e. I0＝2*(VDD-VCM) and/R, and VX2＝VX1＝VCMAnd I is1And I2Is assigned or I1At a constant I0The proportion of the total current is M3Bias voltage V of gridB2It is determined that the lower left circuit 3 and the lower right circuit 4 of fig. 1 cooperate to generate the bias voltage VB2So that I1Value of as I0And exponentially, and the implementation of the specific invention is described below.
The circuit 3 at the lower left corner of the figure 1 consists of a pair of triodes Q with differential structure1And Q2A pair of differential resistors R5/R6Tail current transistor M16And an operational amplifier OP2, the positive input terminal of the operational amplifier OP2 is connected with Q2Branch load resistance R5/R6Is at the output end VX3Negative input terminal of M connected to output terminal of applied common mode voltage VCM, OP216A gate electrode, and M16And Q2Forming a negative feedback loop so that the following relationship holdsX3＝VX2＝VCM. This means that Q2Current I of the branchB2Equal to M in the upper left corner circuit 1 of FIG. 11Current of branch IB2＝I0/2＝(VDD-VCM) This is a constantly controllable value. While Q2Voltage V applied to the baseRIs a reference voltage, Q1The voltage loaded on the base is a linear control voltage VCDue to the nature of the transistor, Q1And Q2Current I of two branchesB1And IB2The following relationship holds:
v in formula (1)TkT/q, k is the Boltzmann constant, q is the electron electric quantity, T is the absolute temperature, i.e. IB1And IB2In an exponential relationship, or IB1And I0In an exponential relationship. I isB1This exponential current is at Q1Resistance R of the branch5/R6On generates a voltage VY1Connected to the positive input of an operational amplifier OP3 of the lower right hand corner circuit 4 of FIG. 1, and generating an offset voltage V by negative feedbackB2The specific design details are as follows. The lower right corner circuit 4 of fig. 1 consists of a differential pair M9/M10，M11/M12And tail current transistor M15A pair of differential resistors R7/R8And an operational amplifier OP3, the values of the transistor and the load resistance element are completely the same as those of the element in the upper right corner circuit 2 of FIG. 1, but the connection mode is slightly different, and in the upper right corner circuit 2, the differential pair M5/M6，M7/M8The two branches are connected in parallel, and the currents of the two branches are gathered to a differential resistor. And in the lower right corner circuit 4, a differential pair M9/M10Connecting differential resistor pairs R7/R8，M11/M12Directly connected to the supply voltage, the purpose of this being to form a current-shunting structure, M9/M10，M11/M12The currents of the two branches are separated, the tail current transistor M in the lower right corner circuit 4 of FIG. 115Gate-loading by a bias voltage V generated in the upper right-hand circuit 2 of FIG. 1B1A pair of differential resistors R7/R8Is short-circuited and connected to the negative input of an operational amplifier OP3, and the positive input of OP3 is connected to the voltage V generated by the lower left corner circuit 3 of fig. 1Y1The output of OP3 generates the critical bias voltage VB2And loaded into differential pair M11/M12Forming a negative feedback loop such that the voltage V isY2And VY1Equal, this means that M9/M10Current I flowing through resistor R in branch1/2 is equal to IB1That is, the following equation holds:
thus, I1And I0Is in exponential relationship and I0Is a constant and controllable value of the electric field,m in the upper left corner circuit 1 of FIG. 1 due to replica biasing1/M2Branch current I1And the total tail current I0In full agreement with the corresponding current in circuit 2, circuit 3, i.e. I in the main amplifier1And I0Also satisfies the relationship of formula (2), and I0＝2*(VDD-VCM) /R is a voltage which can be controlled by controlling the applied common mode voltage VCMTo control the current. Due to I0At VCMFixed is a constant value, then I1Is a function of the control voltage VC-VRLinearly changing and exponentially changing values due to M1Transconductance g of transistorm1Proportional to the current I1To the power of one half of (V), also a function of the control voltage VC-VRLinearly changing and exponentially changing values, so that the gain of the amplifier core circuit in fig. 1 also follows the control voltage VC-VRThe linear change is exponential change, that is, the variable gain amplifying structure satisfies the linear control relation of decibel. The gain expression of the amplifier is as follows:
wherein C isoxIs the unit area capacitance of the transistor gate oxide layer,is M1Width to length ratio of transistor, munIs the mobility of electrons, R is the load resistance, VDDIs the supply voltage, VCMFor applying a common-mode voltage, VRFor controlling the reference voltage, VCControl voltage, V, being linearly variedTK is boltzmann's constant, q is the electron electric quantity, and T is the absolute temperature. The gain of the circuit module is along with the control voltage V according to the formula (3)CThe linear variation is exponential, or decibel linear.
The following provides a new decibel linear variable gain based on the replica bias technique proposed by the present inventionThe specific implementation of the circuit structure adopts a 0.13um CMOS process, and the parameters of each key transistor in the example circuit are shown in Table 1. The operational amplifier in the circuit belongs to common circuit elements, and therefore, the specific description is not provided in the embodiments. The circuit operates at a supply voltage of 1.2V. The circuit was implemented and simulated using the parameters shown in table 1. The simulation results are shown in FIG. 2, and the results show that a common mode voltage V of 0.8V is adopted under a power supply voltage of 1.2VCMAnd a reference voltage V of 0.8VRControl voltage VCThe linear change from 0.8V to 0.9V, the gain of the circuit is changed from-8 dB to 10dB, and the change of the decibel value is linear, namely, the accurate continuous adjustable decibel linear gain control is realized. A plurality of same amplifying units are cascaded to realize a wider gain control range, for example, 4 same amplifying units are cascaded to realize gain control from-32 dB to 40 dB.
Table 1 the present invention provides a new type of continuous adjustable decibel linear variable gain circuit structure parameter table
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose of the embodiments is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All modifications made according to the spirit of the main technical scheme of the invention are covered in the protection scope of the invention.

Claims (10)

1. A continuously adjustable decibel linear variable gain circuit structure, comprising: the amplifier comprises an amplifier core circuit, a common-mode output bias circuit, an exponential proportional current generating circuit and an exponential proportional current bias circuit;
the amplifier core circuit is a differential pair current rudder structure and comprises a differential pair M consisting of field effect transistors M1 and M21/M2Differential pair M consisting of field effect transistors M3 and M43/M4A pair of differential load resistors R1/R2And tail current biasing transistor M13Input differential signal is VIN+/VIN-Respectively connect the differential pair M1/M2A differential signal of VOUT+/VOUT-，VOUT+Connecting M2/M4Drain electrode of (V)OUT-Connecting M1/M3Of the differential pair M1/M2Respectively through a resistor R1/R2Two pairs of differential pairs M connected to a high level VDD1/M2、M3/M4Are respectively connected to the transistor M13Drain electrode of, M13The source of (2) is grounded;
the common mode output bias circuit generates a voltage VB1Loaded in M13A gate electrode;
the exponential proportional current generating circuit is sequentially connected with the exponential proportional current biasing circuit, and the exponential proportional current biasing circuit generates a voltage VB2Loaded in M3/M4A gate electrode; passing voltage VB1And voltage VB2So that the tail current transistor M13Has a bias current of I0Constantly controllable, simultaneously flowing through M1Channel current I of1And I0And is exponential, so that the gain is linearly changed in decibels.
2. The continuous adjustable decibel linear variable gain circuit structure of claim 1 wherein the common mode output bias circuit comprises a differential pair M of fets M5, M65/M6Differential pair M consisting of field effect transistors M7 and M87/M8A pair of differential load resistors R3/R4And tail current biasing transistor M14(ii) a Differential pair M5/M6Grid electrode is connected with external common mode voltage VCM，M7/M8The voltage applied to the gate is derived from a bias voltage V generated by an exponential proportional current bias circuitB2Differential load resistance R3/R4Are shorted together and connected to the positive input of an operational amplifier OP1, and the negative input of OP1 is connected in commonMode voltage VCMVoltage V at output of OP1B1Connect M14Forming a negative feedback loop.
3. The structure of claim 2, wherein the common mode output bias circuit forms a negative feedback loop with the amplifier core circuit to force a load resistor R in the common mode output bias circuit3/R4Voltage V at the output terminalX1Is equal to VCMThen V isDD-1/2*I0*R＝VCM，I0Determined by the formula, I0＝2*(VDD-VCM)/R。
4. The continuous adjustable decibel linear variable gain circuit structure of claim 3 wherein the exponential current generation circuit comprises a triode Q1、Q2Composed difference structure triode Q1/Q2A pair of differential resistors R5/R6Tail current transistor M16And an operational amplifier OP 2; the positive input terminal Q of the operational amplifier OP22Output end V of branch load resistor RX3The negative input end is connected with an external common-mode voltage VCMOutput-terminated M of OP216A gate electrode, and M16And Q2Forming a negative feedback loop.
5. The continuous adjustable decibel linear variable gain circuit structure of claim 4 wherein said exponentially proportional current bias circuit comprises a differential pair M of FETs M9, M109/M10Differential pair M consisting of field effect transistors M11 and M1211/M12A pair of differential resistors R7/R8Tail current transistor M15And an operational amplifier OP3, a differential pair M9/M10Connecting differential resistor pairs R7/R8，M11/M12Directly to a supply voltage; tail current transistor M15Gate loading bias generated in common mode output bias circuitVoltage VB1Resistance pair R7/R8Is short-circuited and connected to the negative input of an operational amplifier OP3, and the positive input of OP3 is connected to the voltage V generated by the exponential-proportional current generating circuitY1The output terminal of OP3 generates a bias voltage VB2And loaded into the differential pair M11/M12The gate of (2) constitutes a negative feedback loop.
6. The continuous adjustable decibel linear variable gain circuit structure of claim 3 wherein the differential pair M is between1/M2Differential signal V for gate loadingIN+/VIN-Is also set to V during operationCMDue to the replica bias VB1Relation of (1), M14Gate bias voltage sum M13All gate bias voltages are equal to VB1，M13Tail current of equal to M14Tail current of0I.e. I0＝2*(VDD-VCM) and/R, and VX2＝VX1＝VCM(ii) a Differential pair M1/M2Is set to be I1Differential pair M3/M4Is set to be I2In I1And I2In the distribution relationship of (1), I1At a constant I0The proportion of the total current is M3Bias voltage V of gridB2And (4) determining.
7. The structure of claim 5, wherein the exponential-proportional current generating circuit forms a negative feedback loop such that V isX3＝VX2＝VCM，Q2Current I of the branchB2Equal to M in the core circuit of the amplifier1Current of branch, i.e. IB2＝I0/2＝(VDD-VCM) (ii)/R, which is a constantly controllable value; while Q2Voltage V applied to the baseRIs a reference voltage, Q1The voltage loaded on the base is a linear control voltage VC。
8. The continuous adjustable decibel linear variable gain circuit structure of claim 7 wherein Q is greater1And Q2Current I of two branchesB1And IB2The following relationship holds:
v in formula (1)TkT/q, k is the Boltzmann constant, q is the electron electric quantity, T is the absolute temperature, i.e. IB1And IB2In an exponential relationship, or IB1And I0Presenting an exponential relationship; i isB1This exponential current is at Q1A voltage V is generated across the resistor R of the branchY1Connected to the positive input terminal of an operational amplifier OP3 of the exponential proportional current bias circuit, and generating a bias voltage V by negative feedbackB2。
9. The continuous adjustable decibel linear variable gain circuit structure of claim 8 wherein the exponential current bias circuit forms a negative feedback loop such that the voltage V isY2And VY1Equal, M9/M10Current I flowing through resistor R in branch1/2 is equal to IB1：
Thus, I1And I0In an exponential relationship, wherein I0Is constant and controllable.
10. The continuous adjustable decibel linear variable gain circuit structure of claim 9 wherein the gain expression for the continuous adjustable decibel linear variable gain circuit structure is:
wherein C isoxIs the unit area capacitance of the transistor gate oxide layer,is M1Width to length ratio of transistor, munIs the mobility of electrons, R is the load resistance, VDDIs the supply voltage, VCMIs a common mode voltage, VRFor controlling the reference voltage, VCControl voltage, V, being linearly variedTkT/q, k is Boltzmann constant, q is the electronic quantity, T is the absolute temperature, and the gain of the continuously adjustable decibel linear variable gain circuit structure is dependent on the control voltage VCLinear in decibel.
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