A gain temperature drift frequency characteristic compensation circuit and method

Abstract

The application discloses a gain temperature drift frequency characteristic compensation circuit and method, which comprises a MOS field effect tube, an inductor, a capacitor, a radio frequency choke resistance and a bias circuit. g The bias circuit is connected with the gate of the MOS field effect tube and is used for providing a control voltage V cm that changes with the ambient temperature to the gate of the MOS field effect tube. The inductor and the capacitor are connected in series and are connected with the source of the MOS field effect tube. The radio frequency choke resistance is connected with the source of the MOS field effect tube and is used for providing a bias voltage V to the source of the MOS field effect tube. The drain of the MOS field effect tube serves as a voltage input / output end.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of circuit design, and particularly relates to a gain temperature drift frequency characteristic compensation circuit and method. BACKGROUND

[0002] In wireless communication, gain is an extremely important index of a system, and in-band flatness and temperature characteristic of the gain can greatly affect the performance of the system. The temperature characteristic of the gain refers to the phenomenon that the gain of the system changes with the change of the ambient temperature. Generally, the smaller the temperature characteristic of the gain is, the better, which is beneficial to the stable work of the system in various environments. However, due to the natural temperature characteristic of the physical characteristic (such as the current and transconductance of a transistor) of a basic device, any system will have gain temperature drift, so reducing the gain temperature drift is an important design topic. In addition, the gain temperature drift also has a frequency characteristic, that is, the temperature drift of the same system in a low frequency band is inconsistent with that in a high frequency band, which will lead to the inconsistent performance of the system in the high and low frequency bands, and is also a characteristic to be improved. As shown in the above problem, f1 / f2 is the frequency band of the system, and G_t1 / G_t2 is the gain of the system at temperature t1 / t2, respectively. Figure 1

[0003] The existing method for compensating the gain temperature drift is realized by changing the current of an amplifier circuit. At high temperature, the transconductance of a device becomes small, and a larger bias current is provided for the amplifier to compensate for the decrease of the gain, and at low temperature, the bias current of the amplifier is reduced. The method will make the current of the chip fluctuate greatly at different temperatures, and the fluctuation of the current will worsen other performances of the system, such as the output power. In addition, the method cannot compensate the frequency characteristic of the gain temperature drift, and this defect is particularly obvious in a wideband system. SUMMARY

[0004] The application aims at solving the problem that the temperature fluctuation of the gain in a communication system changes with the frequency, and provides a gain temperature drift frequency characteristic compensation circuit and method.

[0005] The technical scheme is a gain temperature drift frequency characteristic compensation circuit, which comprises a MOS field effect transistor, an inductor, a capacitor, a radio frequency choke resistor and a bias circuit. The bias circuit is connected with the gate of the MOS field effect transistor and is used for providing a control voltage V g that changes with the ambient temperature to the gate of the MOS field effect transistor. The inductor and the capacitor are connected in series and connected with the source of the MOS field effect transistor. The radio frequency choke resistor is connected with the source of the MOS field effect transistor and is used for providing a bias voltage V cm to the source of the MOS field effect transistor. The drain of the MOS field effect transistor is used as a voltage input / output terminal.

[0006] Further, the control voltage V​g is expressed as: V g = b-aT, wherein T is the ambient temperature, b is V g the DC offset of V g , and a is the slope with temperature, a / b can be designed according to different temperature compensation requirements.

[0007] Further, the bias circuit comprises: a first current circuit for generating a current varying with temperature, a second current circuit for generating a current not varying with temperature, a resistor and a buffer; the output end of the first current circuit, the output end of the second current circuit and the resistor are all connected with the positive input end of the buffer, the negative input end of the buffer is connected with the output end of the buffer, and the output end of the buffer outputs a control voltage V g applied to the gate of the MOS field effect tube.

[0008] Further, the first current circuit is a bandgap reference source circuit, and the second current circuit is a bandgap reference source circuit.

[0009] The application further discloses a gain temperature drift frequency characteristic compensation method, comprising:

[0010] A control voltage V g varying with the ambient temperature is provided for the gate of the MOS field effect tube, and a bias voltage V cm is synchronously provided for the source of the MOS field effect tube.

[0011] By changing the gate-source voltage (V g -V cm ) of the MOS field effect tube M1, the resonant frequency point of the LC is changed, the frequency at which the MOS tube temperature compensation resistor is effective is controlled, and thus the frequency characteristic of the temperature drift is compensated.

[0012] Beneficial effects: the circuit structure of the application can significantly and effectively improve the frequency characteristic of the gain temperature drift of the communication system. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a schematic diagram of the gain temperature drift characteristic of the communication system;

[0014] Figure 2 is a structural schematic diagram of the application;

[0015] Figure 3 is a schematic diagram of the temperature characteristic of the gate voltage Vg of M1;

[0016] Figure 4 is a schematic diagram of the temperature characteristic of the equivalent resistance of M1;

[0017] Figure 5 is a schematic diagram of the gain characteristic of the application;

[0018] Figure 6 A schematic diagram of the frequency response of the system gain temperature drift after compensation;

[0019] Figure 7 for Figure 2 A schematic diagram of the bias circuit in the diagram;

[0020] Figure 8 This is a schematic diagram of the high and low temperature gain curves before and after transmit link compensation. Detailed Implementation

[0021] The technical solution of the present invention will now be further described in conjunction with the accompanying drawings and embodiments.

[0022] like Figure 2 As shown, the circuit structure of the present invention includes a MOS field-effect transistor M1, an inductor L1, a capacitor C1, an RF choke resistor Rchoke, and a bias circuit; wherein, the bias circuit provides a control voltage V to the gate of the MOS field-effect transistor M1. g The RF choke resistor Rchoke provides the bias voltage V to the source of the MOSFET M1. cm VIN and VOUT are the input and output voltages of the circuit, respectively.

[0023] The equivalent resistance of MOSFET M1 is:

[0024]

[0025] Where μ is the carrier drift velocity, and C ox W is the gate-source capacitance of MOSFET M1, and W / L is the width-to-length ratio of MOSFET M1. g -V cm V is the gate-source voltage of the MOSFET M1. th This is the threshold voltage of the MOSFET M1.

[0026] like Figure 7 As shown, the bias circuit of the present invention generates a voltage that varies with temperature. Figure 7 In this context, Ipt is a temperature-dependent current, which can be expressed as Ipt = -aT, and Ibg is a temperature-independent current. Both can be generated using a bandgap reference source circuit. Therefore, the voltage across resistor R3 is:

[0027] V3=(Ibg-aT)*R3 (2)

[0028] After passing through the buffer, Vout is obtained and applied to the gate terminal of MOSFET M1. Therefore, the gate terminal voltage can be expressed as Vout. g=b-aT, where T is the ambient temperature, b = Ibg*R3, and a is the temperature coefficient of the current, which can be designed according to requirements.

[0029] Therefore, the equivalent resistance of MOSFET M1 can be expressed as:

[0030]

[0031] As can be seen from equation (2), the equivalent resistance of the MOS field-effect transistor M1 is a value that varies with temperature.

[0032] The impedance to ground of the entire circuit of this invention can be expressed as:

[0033]

[0034] The impedance to ground of the entire circuit in this invention is a value that changes with temperature and frequency.

[0035] Inductor L1 and capacitor C1 resonate at frequency f2, therefore f2 is called the resonant point of inductor L1 and capacitor C1. At the resonant point f2, the impedance Z1 to ground mainly depends on the impedance R of MOSFET M1. The temperature characteristics of the resistor determine the temperature characteristics of the attenuation, so it exhibits the temperature characteristics of the impedance R of MOSFET M1. As the frequency moves away from the resonant point f2, the temperature characteristics of the impedance Z1 to ground gradually weaken, and the corresponding temperature characteristics of the attenuation also weaken, thus achieving... Figure 5 The gain characteristics are shown.

[0036] like Figure 4 and Figure 5 As shown, the compensation circuit of the present invention is characterized by:

[0037] 1) At temperature t2, the impedance R of MOSFET M1 is: Figure 4 R2 in the equation is a relatively large value; this resistor shields the frequency characteristics of the LC circuit, such as... Figure 5 As shown, the attenuation exhibited by the present invention remains almost constant within the frequency range f1-f2.

[0038] 2) At temperature t1, the impedance R of MOSFET M1 is: Figure 4 R1 in the equation is a relatively small value. Figure 5 At point f1, LC exhibits a large impedance and low attenuation, while at the resonant point f2, Z1 equals R1, resulting in significant attenuation.

[0039] Will Figure 1 and Figure 5 After cascading the gain characteristics in the middle, a result close to the desired value can be obtained. Figure 6 The gain characteristics in the frequency response compensate for the gain temperature drift throughout the entire frequency band.

[0040] At the frequency point with large temperature drift, the LC resonates at the frequency point, and the impedance of LC-Rchoke is basically determined by Rchoke. The temperature characteristic of Rchoke is determined by the temperature characteristic of Vg. Generally, the higher the temperature, the larger Rchoke. Through such design, Rchoke effectively reduces the temperature drift at the frequency point.

[0041] At the frequency point with small temperature drift, since it is far from the resonant frequency of LC, the impedance of LC-Rchoke is basically determined by the resonant impedance of LC, which has no temperature characteristic, so the original temperature drift characteristic is almost not changed at the frequency point.

[0042] Through the above design, the temperature drift of the frequency point with small temperature drift is not changed, and the temperature drift of the frequency point with large temperature drift is reduced, that is, the frequency characteristic of temperature drift is compensated.

[0043] As shown in Figure 8 An example of application of the present application is shown. The curves shown in the figure are the link gain of a transmitting chain, a total of 6 curves are given, which are the high and low temperature gain curves before and after compensation (-40 / 35 / 110℃). It can be seen that:

[0044] Before compensation, the gain difference between low temperature and high temperature at 6GHz is 1.6dB, and at 12GHz is-0.9dB, and the gain temperature drift at the two frequency points is 2.5dB;

[0045] After compensation, the gain difference between low temperature and high temperature at 6GHz is 1.9dB, and at 12GHz is 1.7dB, and the gain temperature drift at the two frequency points is 0.2dB;

[0046] Before and after compensation, the frequency characteristic of the gain temperature drift of the system is obviously improved.

Claims

1. A method for compensating for gain temperature drift frequency response, characterized in that: include: Construct a gain temperature drift frequency response compensation circuit; Provide a control voltage V that varies with ambient temperature to the gate of the MOSFET. g ; Provide a bias voltage V to the source of the MOSFET cm ; By changing the gate-source voltage (V) supplied to the MOSFET M1 g -V cm By changing the resonant frequency of the LC circuit, the effective frequency of the temperature compensation resistor of the MOS field-effect transistor (M1) is controlled, thereby compensating for the frequency characteristics of temperature drift. The gain temperature drift frequency characteristic compensation circuit includes a MOS field-effect transistor (M1), an inductor (L1), a capacitor (C1), an RF choke resistor (Rchoke), and a bias circuit; the bias circuit is connected to the gate of the MOS field-effect transistor (M1) and is used to provide a control voltage V that varies with ambient temperature to the gate of the MOS field-effect transistor (M1). g The inductor (L1) and capacitor (C1) are connected in series and then to the source of the MOS field-effect transistor (M1); the RF choke resistor (Rchoke) is connected to the source of the MOS field-effect transistor (M1) and is used to provide a bias voltage V to the source of the MOS field-effect transistor (M1). cm ; The drain of the MOS field-effect transistor (M1) serves as the voltage input / output terminal; The bias circuit includes: a first current circuit for generating a temperature-dependent current, a second current circuit for generating a temperature-independent current, a resistor (R3), and a buffer; the output terminals of the first and second current circuits and the resistor are all connected to the positive input terminal of the buffer, the negative input terminal of the buffer is connected to the output terminal of the buffer, and the output terminal of the buffer outputs a control voltage V. g The control voltage V is applied to the gate of the MOS field-effect transistor (M1); g Represented as: V g = b - aT, where T is the ambient temperature and b is the temperature in V. g The DC offset, where a is the control voltage V g The slope with temperature.

2. The gain temperature drift frequency response compensation method according to claim 1, characterized in that: The first current circuit is a bandgap reference source circuit, and the second current circuit is a bandgap reference source circuit.

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