JPH1075137A - Variable gain amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable gain amplifier in which an NF(noise figure) does not deteriorate even when a gain is varied, power consumption can be reduced, and a signal with a large amplitude can be handled with low distortion. SOLUTION: A resistor Rg is connected between the inversion input terminal of an operating amplifier U and a ground, a pin diode D1 is connected through a capacitor C1 , and the cathode of the pin diode D1 is grounded. The anode of the pin diode D1 is connected through a resistor R3 with a gain control terminal C to which a variable voltage is impressed. Here, the resistance value of the resistor R3 is sufficiently larger than the resistance value of a resistor Rg . When a voltage Vc of the gain control terminal C is varied, currents flouring through the pin diode D1 are changed, and high-frequency resistance Rd of the pin diode D1 is changed. Thus, a gain can be varied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable gain amplifier in a spectrum analyzer, a network analyzer, and the like.

[0002]

2. Description of the Related Art FIG. 3 is a general configuration diagram of a spectrum analyzer. The input signal RF is frequency-converted by an oscillator Local1 and a mixer Mix1, and an appropriate frequency I
After being converted by F1, it passes through a band-pass filter BPF1. The signal passing through the band-pass filter BPF1 is frequency-converted by the oscillator Local2 and the mixer Mix2, converted into an appropriate frequency IF2, passed through the band-pass filter BPF2, and amplified by the amplifier AMP1. The signal amplified by the amplifier AMP1 is an oscillator Loca
l3 and a mixer Mix3, frequency-converted to an appropriate frequency IF3, and then a band-pass filter BPF
3 and is amplified by the amplifier AMP2. Amplifier AM
The signal that has passed through P2 is the oscillator Local4 and the mixer Mi.
x4, and is converted to an appropriate frequency IF4. The power is detected by the detector DT from the signal of the frequency IF4 and displayed on the display DS.

FIG. 4 is a circuit diagram of the amplifier AMP2 in FIG. Amplifier AMP2 is a gain control amplifier,
Capacitors C ₁₁ , C ₁₂ , C ₁₃ , C ₁₄ and resistors R ₁₁ , R ₁₂ ,
And _{R 13, R 14, R 15} , R 16, R 17, and pin diode D _11, D _12, is composed of a transistor Q.

[0004] The voltage V _A of the gain control A variable, the current flowing is changed to the pin diode D _11, by high-frequency resistance of the pin diode D ₁₁ is changed, the gain between the input and output input signal is attenuated Can be changed. When a voltage V _B of the gain control terminal B variable, similarly, the high frequency resistance is changed in the pin diode D _12, the gain can be variable current feedback amount of the amplifier composed of transistor Q is changed.

[0005]

In the above-mentioned conventional variable gain amplifier, when the gain is lowered, the NF (noise figure) deteriorates, and since the amplifier using the transistor Q is a class A amplifier, a low distortion amplifier can be realized. Had a problem of high power consumption and poor efficiency.

[0006] An object of the present invention is to provide a NF even when the gain is varied.
It is an object of the present invention to provide a variable gain amplifier which does not change (does not deteriorate), consumes low power, and can handle a large amplitude signal with low distortion.

[0007]

According to the variable gain amplifier of the present invention, an input signal is applied to a non-inverting input terminal, an inverting input terminal is connected via a grounding resistor, and one end is a feedback of the operational amplifier. A capacitor connected to a connection point between the resistor and the grounding resistor, a pin diode having an anode connected to the other end of the capacitor, a cathode grounded, and a resistor having one end connected to the anode of the pin diode; It has a gain control terminal connected to the other end of the resistor to which a variable voltage is applied, and the resistance of the resistor is sufficiently larger than the resistance of the grounding resistor.

When the voltage applied to the gain control terminal is varied, the current flowing through the pin diode changes to change the high-frequency resistance of the pin diode, and the combined resistance of the grounding resistor and the high-frequency resistance of the pin diode changes to change the gain. I do.

In this case, the NF of the amplifier is determined by the input resistance and the noise characteristics of the operational amplifier itself. Therefore, if the combined resistance is made sufficiently small, the NF does not change (does not deteriorate) even if the gain is changed.

[0010] Another variable gain amplifier of the present invention comprises:
An input signal having an input signal applied to a non-inverting input terminal, an inverting input terminal connected via a grounding resistor, and a first capacitor having one end connected to a connection point between the feedback resistor of the operational amplifier and the grounding resistor. A first resistor having one end connected to the other end of the first capacitor and the other end grounded; and a pin diode having a cathode connected to a connection point between the first capacitor and the first resistor. And one end is connected to a connection point between the feedback resistor and an output terminal of the operational amplifier,
A second terminal having the other end connected to the anode of the pin diode;
, A second resistor having one end connected to the other end of the second capacitor and the anode of the pin diode, and a gain control connected to the other end of the second resistor and applied with a variable voltage. A resistance value of the first resistor is sufficiently larger than a resistance value of the pin diode and a resistance value of the grounding resistor, and a resistance value of the second resistor is sufficiently larger than a resistance value of the feedback resistor. large.

Also in this case, when the voltage applied to the gain control terminal is varied, the current flowing through the pin diode changes to deteriorate the high-frequency resistance of the pin diode, and the combined resistance of the feedback resistor and the high-frequency resistance of the pin diode changes. Gain changes.

[0012]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of a variable gain amplifier according to one embodiment of the present invention.

U is a high frequency compatible operational amplifier, R ₁ , R ₂
Is an input / output impedance switching resistor. Resistor R _g between the ground and the inverting input terminal of the operational amplifier U is connected, the pin diode D further through the capacitor C _1
1 is connected, the cathode of the pin diode D ₁ is grounded. The anode of the pin diode D ₁ via the resistor R _3, a variable voltage is connected to the gain control terminal C is applied. Here, the resistance value of the resistor R ₃ is sufficiently larger than the resistance value of the resistor R _g.

[0015] The voltage V _c of the gain control terminal C is variable, changes the current flowing through the Pindaoiodo D _1, the high frequency resistance of R _d of the pin diode D ₁ is changed. Here, the combined resistance of the resistors R _d and R _g is represented by R _G (= R _g
× R _d / (R _g + R _d )), the amplifier gain G
(= V ₂ / V ₁₎ than the formula of the operational amplifier _{G = V 2 / V 1 =} {1+ (R f / R G} V 3 / V 1 = (1/2) {1+ (R f / R G ｝

[0016] Thus, when varying the voltage V _c, can be varied gain G combined resistance R _G is changed.

[0017] and variable gain amplifier NF is input resistors R ₁ and R _G, since it is determined by the noise characteristics of the operational amplifier U ₁ itself, if sufficiently small resistance value R _G, even if the gain G variable and, NF Does not get worse. Also, the operational amplifier has low power consumption and can handle large amplitude signals with low distortion.
Power supply efficiency is improved.

FIG. 2 is a circuit diagram of a variable gain amplifier according to another embodiment of the present invention.

In this embodiment, the capacitor C ₁ and the resistor R ₄ are connected in series between the connection point of the ground resistor R _g and the feedback resistor R _f and the ground, and the feedback resistor R _f and the output terminal of the operational amplifier U ₁ are connected. a connection point, the capacitor C ₂ and the pin diode D ₁ between the connection point of the capacitor C ₁ and the resistor R ₄ are connected in series, the resistor R ₃ is connected to a connection point of the capacitor C ₂ and the pin diode D _1, the other end C ₃ of the resistor R ₃ has a gain control terminal C of the variable voltage is applied.

Here, the resistance of the resistor R ₄ is equal to the resistance of the grounding resistor R.
_g , which is sufficiently larger than the resistance value of the feedback resistor R _f and the resistor R ₃
Is sufficiently larger than the resistance value of the feedback resistor _Rf .

The gain G of the operational amplifier U (= V ₂ / V ₁ )
Is the feedback resistance R _f and the high-frequency resistance R of the pin diode D _1.
The combined resistance of _d is R _F (= R _f · R _d / (R _f + R _d ))
G = (V ₂ / V ₁ ≒ 1 + (R _F / R _g )

Therefore, the gain control terminal C
Voltage V_c Is variable, the combined resistance R _F Changes and gain
G can be varied.

[0023]

As described above, according to the present invention, an operational amplifier, a pin diode, and a resistor are combined to vary the gain of an amplifier, thereby providing a variable gain amplifier with low distortion and no deterioration in NF. is there.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a variable gain amplifier according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a variable gain amplifier according to another embodiment of the present invention.

FIG. 3 is a general configuration diagram of a spectrum analyzer.

FIG. 4 is a circuit diagram of a variable gain amplifier in FIG. 3;

[Explanation of symbols]

U op R _1, R ₂ input and output impedance for slip quenching resistor R _f feedback resistor R _g grounding resistors R _3, R ₄ resistors C _1, C ₂ capacitors D _11, D ₁₂ pin diode C gain control terminal

Claims (2)

[Claims] An input signal is applied to a non-inverting input terminal,
An operational amplifier having an inverting input terminal connected via a grounding resistor, a capacitor having one end connected to a connection point between the feedback resistor of the operational amplifier and the grounding resistor, and an anode connected to the other end of the capacitor; A grounded pin diode, one end of which has a resistor connected to the anode of the pin diode, and a gain control terminal connected to the other end of the resistor and to which a variable voltage is applied. A variable gain amplifier that is sufficiently larger than a resistance value of the grounding resistor. 2. An input signal is applied to a non-inverting input terminal,
An operational amplifier having an inverting input terminal connected via a grounding resistor, a first capacitor having one end connected to a connection point between the feedback resistor of the operational amplifier and the grounding resistor, and one end having the other end of the first capacitor. A first resistor connected to one end and the other end grounded; a pin diode having a cathode connected to a connection point between the first capacitor and the first resistor; and one end connected to the feedback resistor and the operational amplifier. A second capacitor connected to a connection point of the output terminal, the other end of which is connected to the anode of the pin diode; and a second capacitor, one end of which is connected to the other end of the second capacitor and the anode of the pin diode. A resistor connected to the other end of the second resistor and a gain control terminal to which a variable voltage is applied;
A variable gain amplifier wherein the resistance of the resistor is sufficiently larger than the resistance of the pin diode and the resistance of the grounding resistor, and the resistance of the second resistor is sufficiently larger than the resistance of the feedback resistor.