JP2017208635A - Low Noise Amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low noise amplifier capable of amplifying an input signal without degrading noise characteristics and distortion characteristics.SOLUTION: The low noise amplifier includes: a low noise amplifier 3 connected between a signal input terminal 1 and a signal output terminal 2; a buffer circuit 4 receiving a signal input into the signal input terminal 1 with a high input impedance and outputs with a low output impedance; a detector circuit 6 detecting the output signal of the buffer circuit 4; and a control circuit 7 controlling a gain of the low noise amplifier according to a level of a detection voltage output from the detector circuit 6.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a low noise amplifying apparatus that amplifies and outputs a low level input signal.

  When receiving a high-frequency signal for digital television or the like, if the level of the input signal is small, the input signal is amplified and then sent to a subsequent stage such as a tuner. When the level of the input signal is high, it is not amplified or attenuated in order to prevent the latter stage tuner and the like from being saturated by the amplified signal.

  Patent Document 1 proposes that an input signal is amplified by an amplifier when the level of a detection voltage obtained by detecting a signal on the output side of the amplifier is small, and that the input signal bypasses the amplifier when the level is large. . Further, Patent Document 2 proposes that the amplifier be operated as an amplifier when the level of the detection voltage obtained by detecting the signal on the output side of the amplifier is small, and that the amplifier be operated as an attenuator when it is large. In Patent Document 2, it is further proposed to detect the signal on the input side of the amplifier and perform the same processing.

JP 2009-260831 A JP 2006-340255 A

  However, in Patent Documents 1 and 2, since the detection circuit that generates a control signal for amplifying, bypassing, or attenuating the amplifier is directly connected to the high-frequency signal line, noise characteristics of the high-frequency signal are obtained. And distortion characteristics may be deteriorated. In particular, when a detection circuit is connected to the input side of the amplifier, the possibility increases because the input signal level is low.

  An object of the present invention is to provide a low noise amplifying apparatus that can amplify an input signal without deteriorating noise characteristics and distortion characteristics.

  To achieve the above object, the invention according to claim 1 is a low noise amplifier connected between a signal input terminal and a signal output terminal, and receives a signal input to the signal input terminal with a high input impedance. A buffer circuit that outputs with a low output impedance; a detection circuit that detects an output signal of the buffer circuit; and a control circuit that controls the gain of the low-noise amplifier according to the level of the detection voltage output from the detection circuit. It is characterized by providing.

  The invention according to claim 2 is a low noise amplifier connected between a signal input terminal and a signal output terminal, first switch means connected between the signal input terminal and the signal output terminal, and the signal A buffer circuit that receives a signal input to the input terminal with a high input impedance and outputs it with a low output impedance, a detection circuit that detects an output signal of the buffer circuit, and a level of a detection voltage that is output from the detection circuit is high. And a control circuit that turns on the first switch means and turns off the first switch means when the level of the output signal of the detection circuit is small.

  According to a third aspect of the present invention, there is provided a low noise amplifier having an input terminal connected to a signal input terminal, a second switch means connected between the output terminal of the low noise amplifier and the signal output terminal, and a first switch. A second switch for connecting the attenuator between the output terminal of the low noise amplifier and the signal output terminal when in a state, and directly connecting the output terminal of the low noise amplifier to the signal output terminal when in a second switching state; Means, a buffer circuit that receives the output signal of the low noise amplifier with a high input impedance and outputs it with a low output impedance, a detection circuit that detects the output signal of the buffer circuit, and a level of a detection voltage output from the detection circuit The second switch means is set to the first switching state when the detection voltage is large, and the second switching means is set to the second switching state when the level of the detection voltage output from the detection circuit is small. And a control circuit for setting the.

  According to a fourth aspect of the present invention, in the low noise amplifying device according to the first, second, or third aspect, a differential voltage amplifier is connected between the detection circuit and the control circuit. A first diode for detecting a signal output from the buffer circuit; a first bias circuit for applying a predetermined bias voltage to the first diode; a capacitor for smoothing the voltage detected by the first diode; and a second diode. And a second bias circuit that applies the same bias voltage as the bias voltage to the second diode, the detection voltage is output from the first diode, the reference voltage is output from the second diode, The differential voltage amplifier amplifies a difference between the detection voltage and the reference voltage.

  The invention according to claim 5 is the low noise amplifying device according to claim 4, wherein a hysteresis comparator is connected between the differential voltage amplifier and the control circuit.

  According to a sixth aspect of the present invention, in the low noise amplifying apparatus according to the fourth aspect, the differential voltage amplifier is configured by an instrumentation amplifier or a differential amplifier.

  According to a seventh aspect of the present invention, in the low noise amplifying device according to the third aspect, the input impedance of the attenuator is set larger than the output impedance.

  The invention according to claim 8 is the low noise amplifying apparatus according to claim 2, wherein the control circuit stops the operation of the low noise amplifier when the level of the detection voltage output from the detection circuit is large. And

  According to the present invention, a buffer circuit is connected to the input end or output end of the low noise amplifier, the signal passing through the buffer circuit is detected by the detection circuit, and the input signal is amplified and attenuated according to the level of the detection voltage. Since the passage and the like are controlled, it is possible to prevent the detection circuit from deteriorating the noise characteristics and distortion characteristics of the input signal and output signal.

1 is a circuit diagram of a low noise amplifier according to a first embodiment of the present invention. It is a circuit diagram of the buffer circuit 4 of the low noise amplifier of FIG. It is a circuit diagram of the detection circuit 6 of the low noise amplifier of FIG. FIG. 2 is a characteristic diagram of gain and noise figure of the low noise amplifying apparatus of FIG. 1. It is a circuit diagram of the low noise amplifier of the 2nd Example of this invention. 6 is a circuit diagram of a detection circuit 6A and a differential voltage amplifier 8 of the low noise amplifying apparatus of FIG. FIG. 6 is a circuit diagram of another example of the detection circuit 6A and the differential voltage amplifier 8A of the low noise amplification device of FIG. FIG. 8 is an amplification characteristic diagram of the differential voltage amplifier of FIG. 6 and the differential voltage amplifier of FIG. 7. FIG. 6 is an amplification characteristic diagram of the low noise amplifying device of FIG. 5. FIG. 6 is an amplification characteristic diagram when the detection circuit 6A of the low noise amplifier of FIG. 5 is provided on the output side of the low noise amplifier 3. It is a circuit diagram of the low noise amplifier of the 3rd Example of this invention. It is a circuit diagram of the attenuator 10 of the low noise amplifier of FIG. It is a voltage characteristic figure of the output terminal of the low noise amplifier 3 of the low noise amplifier of FIG.

<First embodiment>
FIG. 1 shows the configuration of the low noise amplifying apparatus of the first embodiment. Reference numeral 1 denotes a high-frequency signal input terminal, and 2 denotes a high-frequency signal output terminal. For example, an antenna (not shown) is connected to the input terminal 1, and a tuner (not shown) is connected to the output terminal 2. . A variable gain control type low noise amplifier (LNA) 3 is connected between the input terminal 1 and the output terminal 2. A buffer circuit 4 is connected to the input terminal 1. Reference numeral 5 denotes a detection amplifier that amplifies the output signal of the buffer circuit 4, and reference numeral 6 denotes a detection circuit that detects the signal amplified by the detection amplifier 5. A control circuit 7 controls the gain of the low noise amplifier 3 according to the level of the detection voltage Vs output from the detection circuit 6.

  As shown in FIG. 2, the buffer circuit 4 includes a transistor T1 having a drain connected to the power supply terminal VDD, a gate connected to the input terminal 41, a source connected to the ground terminal GND via the resistor R1, and a source output. It consists of a source follower circuit connected to the end 42. The input terminal 41 is connected to the input terminal 1 in FIG. Although the loss at the input section of the low noise amplifier 3 greatly degrades the noise figure (NF), the buffer circuit 4 prevents the noise figure from being degraded by its high input impedance. In addition, the high input impedance of the buffer circuit 4 prevents the adverse effect on the impedance matching of the low noise amplifier 3. Further, the buffer circuit 4 also suppresses distortion generated in the detection amplifier 5 and the detection circuit 6 from returning to the input side of the low noise amplifier 3.

  As shown in FIG. 3, the detection circuit 6 has anodes connected to the common connection terminals of the bias resistors R2 and R3, the coupling capacitor C1, the smoothing capacitor C2, and the capacitor C1 and the resistor R2. The detection voltage Vs, which is composed of a resistor D3 and a diode D1 whose cathode is connected to the common connection terminal of the capacitor C2, is detected from the high-frequency signal input to the input terminal 61, is output to the output terminal 62. The input terminal 61 is connected to the output terminal of the detection amplifier 5, and the output terminal 62 is connected to the input terminal of the control circuit 7.

  When a diode or a diode made of silicon or GaAs is used as the diode D1, since a forward voltage is high, almost no current flows when there is no bias. Therefore, a bias circuit is formed by the resistors R2 and R3, and a predetermined bias is applied to the diode D1. Is applied. Thereby, even when the level of the high-frequency signal amplified by the detection amplifier 5 is low, the signal can be detected and the detection sensitivity can be increased. The resistor R2 can be replaced by a coil, but when detecting a 40 MHz band signal, a large inductance is required to obtain a necessary impedance.

  The control circuit 7 outputs a control voltage VC1 corresponding to the level of the detection voltage Vs output from the detection circuit 6, and continuously controls the gain of the low noise amplifier 3. FIG. 4 shows the gain characteristic (Gain) and noise figure (NF) of the low noise amplifier 3. The lower the level of the high-frequency signal input to the input terminal 1, the lower the level of the output voltage Vs of the detection circuit 6 and the higher the control voltage VC1 output from the control circuit 7, so the low noise amplifier 3 Gain is automatically controlled so that the level is almost constant.

<Second embodiment>
FIG. 5 shows the configuration of the low noise amplifying apparatus of the second embodiment. The same components as those described with reference to FIG. 6A is a detection circuit that outputs a detection voltage Vs and a reference voltage Vf, 7A is a control circuit that outputs a binary voltage VC2 as a control voltage, and 8 is an amplifier that amplifies the difference between the detection voltage Vs output from the detection circuit 6A and the reference voltage Vf. A differential voltage amplifier 9 is a hysteresis comparator. SW1 is a switch for bypassing the low noise amplifier 3, and is switched by a binary control signal VC2 output from the control circuit 7A. The control signal VC2 from the control circuit 7A also controls the operation of the low noise amplifier 3.

  FIG. 6 is a circuit diagram showing a combination of the detection circuit 6A and the differential voltage amplifier 8. As shown in FIG. The detection circuit 6A includes resistors R2 and R3 constituting the bias circuit described in FIG. 3, capacitors C1 and C2, and diode D1, and resistors R4 and R5 constituting another bias circuit, and resistors R4 and R4. A diode D2 biased with R5 is provided. The detection voltage Vs is output from the cathode of the diode D1, and the reference voltage Vf is output from the cathode of the diode D2. By setting the resistance values such that R2 = R4 and R3 = R5, the bias component of the detection voltage Vs matches the reference voltage Vf. Therefore, Vs = Vf when there is no signal when a high frequency signal is not input. When a high frequency signal is input, Vs> Vf.

  The differential voltage amplifier 8 is configured as an instrumentation amplifier having high input impedance by the operational amplifiers OP1, OP2, OP3 and the resistors R6, R7, R8, R9, R10, R11, and is based on the detection voltage Vs input from the detection circuit 6A. A signal obtained by subtracting the voltage Vf is amplified. Thus, by subtracting the reference voltage Vf, which is the bias component, from the detection voltage Vs containing the bias component, the bias component can be canceled and only the detection component can be amplified and taken out from the output terminal 82. .

  FIG. 7 is a circuit diagram in which the differential voltage amplifier 8 is changed to a differential voltage amplifier 8A in the circuit of FIG. The differential voltage amplifier 8A is configured as a differential amplifier by an operational amplifier OP4 and resistors R13, R14, R15, and R16. Although the differential voltage amplifier 8A having this differential amplifier configuration does not have high input impedance, the gain can be reduced as the output voltage increases, so that it can be amplified over a wide input range.

  FIG. 8 shows gain characteristics of the differential voltage amplifier 8 of FIG. 6 and the differential voltage amplifier 8A of FIG. A indicated by a thin line is a characteristic when the differential voltage amplifier 8 (instrumentation amplifier) of FIG. 6 is used, and B indicated by a thick line is a characteristic when the differential voltage amplifier 8A (differential amplifier) of FIG. 7 is used. is there. In the differential voltage amplifier 8A shown in FIG. 7, the reference voltage Vf increases as the output voltage at the output terminal 82 increases. Therefore, the difference between the reference voltage Vf and the detection voltage Vs decreases, and the output terminal 82 The rate of voltage increase decreases. For this reason, it is possible to detect a wider range of input power.

  The hysteresis comparator 9 sets the output voltage to, for example, the L level when the power of the high-frequency signal input to the input terminal 1 (corresponding to the output voltage of the differential voltage amplifiers 8 and 8A) exceeds −50 dBm. Has hysteresis characteristics such as setting to level.

  When the output voltage of the hysteresis comparator 9 becomes L level, the control circuit 7A turns on the switch SW1 and turns off the operation of the low noise amplifier 3. At this time, the insertion loss of the switch SW1 is, for example, -1 dB. Further, when the output voltage of the hysteresis comparator 9 becomes H level, the switch SW1 is turned OFF and the gain of the low noise amplifier 3 is set to 20 dB. Therefore, the total gain by the switch SW1 and the low noise amplifier 3 has hysteresis characteristics as shown in FIG. 9, and can be switched stably.

  Thus, in this embodiment, since the input power is detected by detecting the high frequency signal at the input end of the low noise amplifier 3, it is only necessary to detect a signal in the range of −60 dBm to −50 dBm.

  On the other hand, when switching is performed using a signal obtained by detecting the high-frequency signal at the output terminal of the low noise amplifier 3, assuming that the gain of the low noise amplifier 3 is 20 dB and the loss of the switch SW1 is −1 dB, FIG. Thus, it is necessary to detect a high-frequency signal in a wide range of −61 (= −60−1) dBm to −30 (= −50 + 20) dBm, and high performance is required for the detection circuit 6A.

<Third embodiment>
FIG. 11 shows the configuration of the low noise amplifying apparatus of the third embodiment. In this embodiment, the gain of the low noise amplifier 3 is fixed, the output signal is taken in by the buffer circuit 4, amplified by the detection amplifier 5, detected by the detection circuit 6A, amplified by the differential voltage amplifier 8, and the hysteresis comparator 9 The control circuit 7A outputs a binary control signal VC2. Reference numeral 10 denotes an attenuator connected to the output side of the low-noise amplifier 3, and switches SW2 and SW3 (switch means) are connected to the input end and output end of the low-noise amplifier 3, and are inserted into the high-frequency signal line by switching the switches SW2 and SW3. Or bypassed.

  The gain of the low noise amplifier 3 is set to 20 dB. When the input power is −60 dBm, the output power of the low noise amplifier 3 is −40 dBm, and when the input power is −50 dBm, the output power of the low noise amplifier 3 is -30 dBm. Therefore, at this time, the detection circuit 6A only needs to detect a signal in the range of −40 dBm to −30 dBm, and therefore the gain of the detection amplifier 5 can be small. As in the circuit of FIG. 5, when the input power exceeds −50 dBm, the output of the hysteresis comparator 9 becomes L level, and the control circuit 7A switches the switches SW2 and SW3 to select the attenuator 10. If the input power falls below −60 dBm, the output of the hysteresis comparator 9 becomes H level, and the switches SW2 and SW3 are switched to bypass the attenuator 10 by the control circuit 7A.

  The attenuator 10 may set its input impedance Zin and output impedance Zout to 50Ω as usual, but the voltage level input to the buffer circuit 4 can be increased by increasing the input impedance.

  FIG. 12 is a diagram showing a configuration of the attenuator 10, which includes resistors R 17, R 18, and R 19 that form a T-shaped circuit between the input terminal 101 and the output terminal 102. For example, when R17 = 480Ω, R18 = 22.4Ω, and R19 = 28.4Ω are set, the input impedance Zin = 500Ω and the output impedance Zout = 50Ω, and a 21 dB attenuator can be realized.

  If the input impedance Zin of the attenuator 10 is set to a large value in this way, when the switches SW2 and SW3 are switched from the state in which the attenuator 10 is bypassed to the state in which the attenuator 10 is connected, the signals pass through the buffer circuit 4 and the detection amplifier 5. Since the high-frequency voltage input to the detection circuit 6A is increased, the hysteresis characteristic as shown in FIG. 13 can be realized in the voltage at the output terminal of the low noise amplifier 3. Therefore, in this case, the hysteresis comparator 9 can be replaced with a normal comparator having no hysteresis characteristic.

<Other examples>
1, the detection circuit 6 is changed to the combination of the detection circuit 6A and the differential voltage amplifier 8 described in FIG. 6, or the combination of the detection circuit 6A and the differential voltage amplifier 8A described in FIG. can do.

1: input terminal, 2: output terminal, 3: low noise amplifier, 4: buffer circuit, 5: detection amplifier, 6, 6A: detection circuit, 7, 7A: control circuit, 8, 8A: differential voltage amplifier, 9 : Hysteresis comparator, 10: Attenuator

Claims (8)

  A low noise amplifier connected between the signal input terminal and the signal output terminal; a buffer circuit that receives a signal input to the signal input terminal with a high input impedance and outputs the signal with a low output impedance; and an output signal of the buffer circuit And a control circuit for controlling the gain of the low-noise amplifier in accordance with the level of the detection voltage output from the detection circuit.   A low noise amplifier connected between the signal input terminal and the signal output terminal, a first switch means connected between the signal input terminal and the signal output terminal, and a signal input to the signal input terminal A buffer circuit that receives an input impedance and outputs a low output impedance; a detection circuit that detects an output signal of the buffer circuit; and when the level of a detection voltage output from the detection circuit is large, the first switch means is turned on, And a control circuit for switching the first switch means to turn off when the level of the output signal of the detection circuit is small.   A low noise amplifier having an input terminal connected to the signal input terminal; an attenuator connected between the output terminal of the low noise amplifier and the signal output terminal; and an output terminal of the low noise amplifier in the first switching state. A second switch means for connecting the attenuator between the signal output terminal and the output terminal of the low noise amplifier directly to the signal output terminal in the second switching state; and an output signal of the low noise amplifier. A buffer circuit that receives a high input impedance and outputs a low output impedance; a detection circuit that detects an output signal of the buffer circuit; and a second switching means that detects the level of a detection voltage output from the detection circuit is high. A control circuit that sets the second switch means to the second switching state when the level of the detection voltage that is set to one switching state and is output from the detection circuit is small. Low-noise amplifier according to claim Rukoto. In the low noise amplifying device according to claim 1, 2, or 3,
A differential voltage amplifier is connected between the detection circuit and the control circuit;
The detection circuit smoothes a voltage detected by the first diode, a first diode for detecting a signal output from the buffer circuit, a first bias circuit for applying a predetermined bias voltage to the first diode, and the first diode. A capacitor, a second diode, and a second bias circuit that applies the same bias voltage as the bias voltage to the second diode, the detection voltage is output from the first diode, and a reference is generated from the second diode. Voltage is output,
The differential voltage amplifier amplifies a difference between the detection voltage and the reference voltage;
A low noise amplifying device. The low noise amplifying device according to claim 4,
A low noise amplification device, wherein a hysteresis comparator is connected between the differential voltage amplifier and the control circuit. The low noise amplifying device according to claim 4,
The differential voltage amplifier comprises an instrumentation amplifier or a differential amplifier. The low noise amplifying device according to claim 3,
The attenuator has a low noise amplifying device in which an input impedance is set larger than an output impedance. The low noise amplifying device according to claim 2,
The control circuit stops the operation of the low noise amplifier when the level of the detection voltage output from the detection circuit is large.

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