JP4214348B2 - Variable gain low noise amplifier - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a variable gain low noise amplifier, and more particularly to a gain control type low noise amplifier of a reception RF front end unit in a communication device such as a television, a radio, a CATV, or a mobile radio.
[0002]
[Prior art]
Recently, services such as various wireless systems, wireless telephones, satellite broadcasting, CATV, digital TV, and satellite broadcasting have been provided.
[0003]
The low frequency part, baseband part, and digital processing part of the ICs that make up these systems have been exclusively silicon CMOS, which has a high degree of integration and low power consumption. However, recent fine gate technology uses CMOS as a gigahertz RF. It can be applied to bands, and it is becoming possible to create a one-chip wireless system including these. Providing many ICs at a low price is the key to the popularization of wireless systems, and such a flow is inevitable.
[0004]
The RF receiving function block connected next to the antenna of the wireless system is a low noise amplifier. The low noise amplifier is said to be an important block that determines the noise figure of the entire receiver, that is, how small the input signal can be received. Furthermore, in recent complex digital modulation radio systems and direct conversion receiver configurations, it is necessary to handle radio waves with various input sensitivities as signals of a certain level, and the amplifier is required to have a high gain control function.
[0005]
As a front-end variable gain amplifier using a silicon field effect transistor, for example, a circuit using a dual gate field effect transistor for a TV tuner as disclosed in JP-A-6-1777785 is widely used. .
[0006]
FIG. 11 shows an example of a dual gate or cascode connection type field effect transistor amplifier. The high frequency signal input from the terminal RFin is amplified and appears at the terminal RFout. The gain can be controlled by terminals Vg and Vc. In this configuration, in particular, the operating region of the cascode-connected field effect transistor 1203 is changed in the triode region by changing the voltage of the terminal Vc, and the gain is controlled by changing the mutual conductance of the field effect transistor 1203. Many.
[0007]
[Problems to be solved by the invention]
However, as shown in FIG. 12, when the relationship between the minimum noise figure (NFmin) of the field effect transistor obtained by measurement and the measurement bias condition is seen, NFmin is 1 decibel (dB) or less when biased in the saturation region. Although it is very small, there is a problem that NFmin deteriorates rapidly when entering the triode region. Therefore, for low noise operation, it is preferable to control not only the terminal Vc but also the terminal Vg to control the gain, but the two terminals must be controlled simultaneously, which is very difficult to use.
[0008]
A GaAs field effect transistor is mounted on a printed circuit board or a ceramic substrate together with a plurality of components constituting a bias circuit and a control circuit. In such a mounting board, there are problems of many man-hours for assembly and adjustment and high cost in order to supply a very large number of wireless systems.
[0009]
An object of the present invention is to provide a low-noise amplifier having a high added value of a gain control function while maintaining low noise while reducing the number of external parts in a CMOS wafer process.
[0010]
[Means for Solving the Problems]
According to the present invention, is connected to the source electrode of the drain electrode and the second field effect transistor of the first field effect transistor, the first source electrode of the field-effect transistor is grounded, the second field effect A drain electrode of the transistor is connected to a DC power source through a load, a signal is input using the gate electrode of the first field effect transistor as a signal input terminal, and the drain electrode of the second field effect transistor is output as a signal in cascoded amplifier that outputs a signal as a terminal, a first terminal for connecting the gate electrode and the drain electrode of the third field-effect transistor and a source electrode of the fourth field-effect transistors, said first field effect A gate electrode of the transistor is connected via a resistor, and a source electrode of the third field effect transistor is connected. Is, a control unit for the drain electrode is composed of the said third and fourth field effect transistors which are connected to a DC power source of the fourth field-effect transistor, said fourth field effect transistor A variable gain low noise amplifier is obtained , wherein the gain of the cascode-connected amplifier is controlled by the voltage of the second terminal to which the gate electrode and the gate electrode of the second field effect transistor are connected .
[0011]
Further, according to the present invention, is connected to the source electrode of the drain electrode and the second field effect transistor of the first field effect transistor, the first source electrode of the field effect transistor is grounded, the second A drain electrode of the field effect transistor is connected to a DC power source through a load, a signal is input using the gate electrode of the first field effect transistor as a signal input terminal, and the drain electrode of the second field effect transistor is signaled In the cascode-connected amplifier that outputs a signal as the output terminal of the first resistor, the drain electrode of the third field-effect transistor and one terminal of the first resistor are connected, and the other terminal of the first resistor (hereinafter referred to as “the first resistor”). 1 terminal) is connected to the gate electrode of the third field effect transistor and the source electrode of the fourth field effect transistor, The first terminal and the gate electrode of the first field effect transistor are connected via a second resistor, the source electrode of the third field effect transistor is grounded, and the fourth field effect transistor a control unit for the drain electrode is composed of said first resistor and said third and said fourth field effect transistor which are connected to a DC power source, said gate electrode of said fourth field-effect transistor A variable gain low noise amplifier is obtained , wherein the gain of the cascode-connected amplifier is controlled by the voltage at the second terminal connected to the gate electrode of the second field effect transistor.
[0012]
Further, according to the present invention, is connected to the source electrode of the drain electrode and the second field effect transistor of the first field effect transistor, the first source electrode of the field effect transistor is grounded, the second A drain electrode of the field effect transistor is connected to a DC power source through a load, a signal is input using the gate electrode of the first field effect transistor as a signal input terminal, and the drain electrode of the second field effect transistor is signaled In the cascode-connected amplifier that outputs a signal as an output terminal of the first, the drain electrode of the third field effect transistor and the cathode of a diode that generates a constant voltage are connected, and the anode of the diode (hereinafter referred to as “first terminal”) that.) a source conductive gate electrode and the fourth field effect transistor of the third field-effect transistor Connected to bets, wherein the first terminal and the first gate electrode of the field effect transistor is connected via a resistor, the third source electrode of the field effect transistor is grounded, said fourth field effect a control unit for the drain electrode is composed of the said third and fourth field effect transistors which are connected to a DC power source and the diodes of transistors, the gate electrode of said fourth field-effect transistor the A gain-variable low-noise amplifier is obtained in which the gain of the cascode-connected amplifier is controlled by the voltage of the second terminal connected to the gate electrode of the second field effect transistor.
[0013]
Further, according to the present invention, is connected to the source electrode of the drain electrode and the second field effect transistor of the first field effect transistor, the first source electrode of the field effect transistor is grounded, the second A drain electrode of the field effect transistor is connected to a DC power source through a load, a signal is input using the gate electrode of the first field effect transistor as a signal input terminal, and the drain electrode of the second field effect transistor is signaled In the cascode-connected amplifier that outputs a signal as an output terminal of the third field effect transistor, the drain electrode of the third field effect transistor is connected to the source electrode of the fifth field effect transistor that generates a constant voltage . A gate electrode, a drain electrode, a gate electrode of the third field effect transistor, and a fourth field effect transistor; A gate electrode of the first terminal and the first field effect transistor connected to the source electrode of the static is connected via a resistor, a source electrode of said third field-effect transistor is grounded, the fourth A gate electrode of the fourth field effect transistor, comprising: a control unit including the third, fourth, and fifth field effect transistors, each having a drain electrode of the field effect transistor connected to a DC power source; And a gain of the cascode-connected amplifier is controlled by a voltage of a second terminal to which the second field effect transistor is connected to a gate electrode of the second field effect transistor.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIG. The gate of the field effect transistor 405 of the cascode amplifier composed of the field effect transistors 405 and 406 and the load 407 is connected to the RF signal input section through the capacitor 404 that cuts direct current (DC), and the other is connected to the resistor 403. To the bias circuit section A0 composed of field effect transistors 401 and 402 constituting the bias circuit. The gate of the field effect transistor 402 is connected to its own drain, and is connected to a cascode-connected field effect transistor 405 via a resistor 403 for drawing out to a bias DC voltage source with high impedance. The field effect transistor of the bias circuit section A0 has a drain connected to a DC power supply, a gate connected to the gate of a cascode-connected field effect transistor 406, and is taken out as a gain control terminal. At this time, the voltage of the gain control terminal is set to Vc.
[0017]
The circuit of the bias circuit unit A0 has a sufficiently high DC power supply voltage, and naturally the gate voltage of the field effect transistor 402 is biased to the current saturation region in the voltage range of Vc in which the field effect transistors 401 and 402 operate in the current saturation region. The voltage is on. That is, the bias is applied to the point indicated by the black circle in the current-voltage characteristic of FIG. The gate voltage of the field effect transistor 402 generated in this way is applied to the gate of the field effect transistor 405 through the resistor 403 and the high-pass filter of the capacitor 404. At this time, even if Vc is changed, the field effect transistor 405 of the cascode amplifier is also biased to the current saturation region in a DC manner. In this state, when Vc is changed, the current of the field effect transistor 405 changes along the line connecting the black circles in FIG. As a result, the bias condition of the field effect transistor 405 in which the minimum noise figure shown in FIG. 12 is kept low is set regardless of Vc. The gain of the cascode amplifier is changed by a change in transconductance that changes as the drain current of the field effect transistor 405 changes. Therefore, it can be seen that the gain can be varied and matching using the minimum noise figure can be performed only by controlling Vc.
[0018]
Furthermore, as shown by the arrow in FIG. 4, if the design is to make use of the minimum noise figure by setting the bias point of the field effect transistor 405 in the current saturation region, it is possible to use the bias circuit section as shown in FIG. It becomes. The voltage level may be shifted by inserting a DC voltage source 703 for shifting the voltage level between the gate and drain of the field effect transistor 702 constituting the bias circuit.
[0019]
As another embodiment of the present invention, three examples are shown in FIGS. 6, 7 and 8, respectively. 6 is a circuit in which a resistor is inserted instead of the voltage source 703 in FIG. 5, FIG. 7 is a circuit in which a diode is inserted in place of the voltage source 703 in FIG. 5, and FIG. 8 is a field effect in place of the voltage source 703 in FIG. A voltage shift is realized by a circuit in which a transistor is inserted.
[0020]
In the combination of the cascode amplifier and the bias circuit described so far, the dependency of the gain characteristic on the control voltage Vc is determined by the relationship between the drain current of the field effect transistor 405 and the mutual conductance. Therefore, a desired gain control voltage relationship may not be obtained, and it is necessary to insert a circuit for changing the relationship between Vc and gain.
[0021]
For example, a bias circuit A1 shown in FIG. 1 can be cited as a circuit that changes the relationship between Vc and Vc ′. In this example, the relationship between the gain of decibel display and the control voltage Vc ′ is linear. When the field effect transistor 405 shown in FIG. 3 is biased in the weak inversion region, the transconductance increases in proportion to the current and exponentially with respect to the gate voltage. Therefore, in the bias circuit of the present invention, the gain changes exponentially with respect to Vc in this region, so that the decibel gain change changes linearly with respect to Vc.
[0022]
In the circuit shown in A1 of FIG. 1, when Vc ′ is large, the field effect transistor 103 is turned off, and the relationship between Vc and Vc ′ is given by the ratio of the resistors R1 (102) and R2 (101). Accordingly, the gain change of the decibel is linear with respect to Vc ′ at this time. On the other hand, when the field effect transistor 405 is biased to the strong inversion region, the current dependency of the mutual conductance of the field effect transistor is not simple. In the bias circuit A1 shown in FIG. 1, the current dependence of the mutual conductance of the field effect transistor 405 and the Vc using the nonlinear current-voltage characteristics of the field effect transistor 103 under the condition that the field effect transistor 103 is turned on when Vc ′ is Vcc. Change the relationship of ′. At this time, by carefully selecting the gate width of the field effect transistor 103, the gain of the decibel and Vc ′ can be linearly related. Note that it is necessary to select the resistor R1 (102) and the resistor R2 (101) so that the relationship between this condition and the field effect transistor 103 is well connected.
[0023]
【Example】
FIG. 9 shows an embodiment of the present invention. The input portion of the cascode amplification unit is matched to a target frequency by an inductor and a capacitor. An inductor is used for the load, and it is designed so that a gain can be obtained at a target frequency. A2 employs an example of the bias circuit of the present invention. The conversion circuit unit A1 that changes the relationship between the control voltage and the gain is configured by connecting three stages of inverter circuits of P-channel field effect transistor inputs using an n-channel field effect transistor as a load to the operational amplifier unit. The gate width of the field effect transistor for using the nonlinear characteristic is selected so that the relationship between the control voltage Vc ′ and the gain of the decibel is linear. By matching the input part of the cascode amplifier part under the condition that the minimum noise is obtained, the noise figure of the amplifier can be obtained with a value close to the minimum noise figure of the device. If gain is important, it is sufficient to match the maximum gain.
[0024]
FIG. 10 shows the control voltage dependence of the gain of the embodiment of the present invention. As shown in FIG. 10, the function is such that the voltage Vc saturates at a high gain with respect to the decibel gain, but it has a linear relationship with Vc ′ over a wide range. .
[0025]
In the embodiment, the load of the cascode amplifier may be a matching circuit. The matching circuit including the inductor load may be formed on the same chip as the field effect transistor, or may be a component mounted outside the chip. Similarly, the matching circuit on the input side may be formed on the same chip as the field effect transistor.
[0026]
In the embodiment, even if the part of the bias circuit A0 is replaced with the circuit shown in FIGS. 5, 6, 7, and 8, the basic operation does not change. Since the bias condition of the source grounded field effect transistor of the cascode amplifier becomes a condition of current saturation, a lower noise figure characteristic can be expected. However, a high voltage is required as the power supply voltage.
[0027]
In the above embodiment, the operational amplifier portion may be composed of a CMOS inverter or an n-channel field effect transistor input inverter having a P-channel field effect transistor as a load. Also, an operational amplifier of a type constituted by ordinary differential amplification may be used. What is necessary is just to select according to the setting of a desired DC level.
[0028]
【The invention's effect】
According to the present invention, a high-performance variable gain low noise amplifier can be provided by CMOS technology. By using this technology and making adjustments as little as possible, reducing external parts and reducing costs, and providing them with a one-chip IC, it becomes possible to supply a large number of wireless systems.
[Brief description of the drawings]
FIG. 1 is a diagram showing a basic configuration of a cascode variable gain low noise amplifier according to the present invention.
FIG. 2 is a diagram showing a current saturation region of a field effect transistor together with current-voltage characteristics.
FIG. 3 is a diagram for explaining the operation of the bias circuit of the amplifier of the present invention.
FIG. 4 is a diagram for explaining a method for setting a current saturation bias condition of a field effect transistor to a condition that can obtain a minimum noise figure of the transistor.
5 is a circuit diagram showing an example of a bias circuit for setting a minimum noise figure bias condition as shown in FIG. 4; FIG.
FIG. 6 is a circuit diagram showing another example of a bias circuit for setting the minimum noise figure bias condition as shown in FIG. 4;
7 is a circuit diagram showing still another example of a bias circuit for setting the minimum noise figure bias condition as shown in FIG. 4; FIG.
8 is a circuit diagram showing still another example of a bias circuit for setting the minimum noise figure bias condition as shown in FIG. 4; FIG.
FIG. 9 is a diagram showing an example of a cascode variable gain low noise amplifier according to the present invention.
FIG. 10 is a graph showing the control voltage dependence of gain in the embodiment of the present invention.
FIG. 11 is a diagram showing a basic configuration of a conventional cascode-connected variable gain amplifier using a field effect transistor.
FIG. 12 is a diagram showing current-voltage characteristics of a field effect transistor and the minimum noise figure of the transistor.
[Explanation of symbols]
101 Resistance R2
102 Resistance R1
103 Field Effect Transistors 104 and 105 DC Voltage Source 106 Operational Amplifiers 401 and 402 Field Effect Transistor 403 Resistor 404 Capacitors 405 and 406 Field Effect Transistor 407 Cascode-connected Amplifier Loads 701 and 702 Field Effect Transistor 703 DC Voltage Source 1201 Capacitor 1202 Resistors 1203 and 1204 for drawing out to a bias DC voltage source with high impedance Cascode-connected field effect transistor

Claims (4)

The drain electrode of the first field effect transistor and the source electrode of the second field effect transistor are connected, the source electrode of the first field effect transistor is grounded, and the drain electrode of the second field effect transistor is loaded Is connected to a DC power source, and a signal is input using the gate electrode of the first field effect transistor as a signal input terminal, and a signal is output using the drain electrode of the second field effect transistor as a signal output terminal. In the cascode connection type amplifier,
A first terminal connecting a gate electrode and a drain electrode of the third field effect transistor and a source electrode of the fourth field effect transistor and a gate electrode of the first field effect transistor are connected via a resistor. A control composed of the third and fourth field effect transistors, wherein a source electrode of the third field effect transistor is grounded and a drain electrode of the fourth field effect transistor is connected to a DC power source. Part
The gain of the cascode-connected amplifier is controlled by a voltage at a second terminal to which the gate electrode of the fourth field effect transistor and the gate electrode of the second field effect transistor are connected. Low noise amplifier. The drain electrode of the first field effect transistor and the source electrode of the second field effect transistor are connected, the source electrode of the first field effect transistor is grounded, and the drain electrode of the second field effect transistor is loaded Is connected to a DC power source, and a signal is input using the gate electrode of the first field effect transistor as a signal input terminal, and a signal is output using the drain electrode of the second field effect transistor as a signal output terminal. In the cascode connection type amplifier,
The drain electrode of the third field effect transistor and one terminal of the first resistor are connected, and the other terminal (hereinafter referred to as “first terminal”) of the first resistor is the third field effect. A gate electrode of the transistor and a source electrode of a fourth field effect transistor; and the first terminal and the gate electrode of the first field effect transistor are connected via a second resistor; The field effect transistor includes the third and fourth field effect transistors and the first resistor, wherein the source electrode of the field effect transistor is grounded, and the drain electrode of the fourth field effect transistor is connected to a DC power source. Having a control unit,
The gain of the cascode-connected amplifier is controlled by a voltage at a second terminal to which the gate electrode of the fourth field effect transistor and the gate electrode of the second field effect transistor are connected. Low noise amplifier. The drain electrode of the first field effect transistor and the source electrode of the second field effect transistor are connected, the source electrode of the first field effect transistor is grounded, and the drain electrode of the second field effect transistor is loaded Is connected to a DC power source, and a signal is input using the gate electrode of the first field effect transistor as a signal input terminal, and a signal is output using the drain electrode of the second field effect transistor as a signal output terminal. In the cascode connection type amplifier,
The drain electrode of the third field effect transistor is connected to the cathode of a diode that generates a constant voltage, and the anode (hereinafter referred to as “first terminal”) of the diode is the gate electrode of the third field effect transistor. And the source electrode of the third field effect transistor, the first terminal and the gate electrode of the first field effect transistor are connected via a resistor, and the source electrode of the third field effect transistor Is connected to a DC power source, and has a control unit composed of the third and fourth field effect transistors and the diode.
The gain of the cascode-connected amplifier is controlled by a voltage at a second terminal to which the gate electrode of the fourth field effect transistor and the gate electrode of the second field effect transistor are connected. Low noise amplifier. The drain electrode of the first field effect transistor and the source electrode of the second field effect transistor are connected, the source electrode of the first field effect transistor is grounded, and the drain electrode of the second field effect transistor is loaded Is connected to a DC power source, and a signal is input using the gate electrode of the first field effect transistor as a signal input terminal, and a signal is output using the drain electrode of the second field effect transistor as a signal output terminal. In the cascode connection type amplifier,
The drain electrode of the third field effect transistor is connected to the source electrode of the fifth field effect transistor that generates a constant voltage, and the gate electrode and the drain electrode of the fifth field effect transistor are connected to the third field effect transistor. A first terminal connecting a gate electrode and a source electrode of the fourth field effect transistor and a gate electrode of the first field effect transistor are connected via a resistor, and the source electrode of the third field effect transistor A control unit configured with the third, fourth, and fifth field effect transistors, each of which is grounded, and a drain electrode of the fourth field effect transistor is connected to a DC power source,
The gain of the cascode-connected amplifier is controlled by a voltage at a second terminal to which the gate electrode of the fourth field effect transistor and the gate electrode of the second field effect transistor are connected. Low noise amplifier.

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