KR790001472B1 - Gain control circuit - Google Patents

Abstract

A cct, which could improve characteristics of the gain attenuation quantity VS. noise factor, was composed of transistor(Q2) comprising a signal current source(ei), resistor(Rc) connected to the transistor collector in series, common-base transistor(Q1) whose base was connected to the other lead of the resistor(Rc) and load impedance (RL) connected to the transistor (Q1) collector. A max. gain attenuation quantity was easily determined by the ratio of the resistor (Rc) to variable impedance element (Z1).

Description

Gain control circuit

1 is a connection diagram showing a conventional gain control circuit.

2 is a connection diagram showing a basic configuration of a gain control circuit of the present invention.

3 is a connection diagram showing a specific embodiment of the present invention.

4 through 8 are connection diagrams showing another embodiment of the present invention.

The present invention relates to a gain control circuit, and more particularly, to propose a gain control circuit obtained by easily improving the gain attenuation versus noise characteristics and selecting the maximum attenuation amount to an appropriate value.

Fig. 1 shows a gain control circuit conventionally used in conventional ICs (integrated circuits). The conventional circuit includes a constant current source classify the constant current I _O of the transistor Q ₁ to the circuit transistor Q _2, Q ₃ to the flowing current I _1, and I ₂ to the transistor by the voltage value of the control voltage V _AGC Q _2, each emitter of the flowing Q ₃ each current I _1, by changing the diversion ratio of I ₂ transistors Q _2, Q ₃ site controlling the impedance, the transistor a signal current i _O from the transistor Q ₁ Q _2, Q ₃ It is a circuit for classifying into currents i ₁ and i ₂ flowing in, and varying the signal current i ₂ flowing in the load resistance R _L to control gain.

As the conventional circuit, the noise distribution of the base distribution resistor r _bb '(not shown) of the transistor Q _{3 and} the base distribution resistor r _bb ' (not shown) of the transistor Q ₂ at the time of these attenuations appears at the output. There is a drawback that the deterioration of NF (noise index) occurs.

The present invention proposes and lowers a gain control circuit that can eliminate these drawbacks and improve the attenuation versus noise figure.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

2 shows a basic configuration of the present invention, where I ₀ is a signal current source, Q ₁ is a base ground transistor, R _L is a load impedance, and Z ₁ is a variable impedance element.

In this circuit, the output voltage V _O is

Where Z ₁ 》 Rc, so V _O ≒ i _O · R _L. … … … … … … (4)

The signal current i _O is transferred to the full load impedance R _L to the maximum gain.

Next, the variable current element Z ₁ is impedance controlled by the gain control signal V _AGC , so that the signal current i _O is a resistor.

Rc and is classified as i _1, i ₂ represented by the formula (1) and equation (2) by the ratio of the size of the variable impedance element Z _1. For this reason, the output voltage _VO becomes the value represented by Formula (3) above, and the gain is attenuated.

When the variable impedance element Z ₁ becomes Z ₁ = 0, the output signal current i ₂ becomes i ₂ = 0 from the formula (1) and the output signal voltage V ₀ = 0 to obtain the maximum attenuation amount.

Thus, the gain control but is performed with the present invention the output according to the circuit noise by the base distributed resistance r _bb 'of the transistor Q ₁ will therefore have little benefit for the output by a resistor R _C connected to the emitter of the transistor Q ₁ It does not appear effectively. This attenuation versus noise figure characteristics can be improved from the conventional circuit shown in FIG.

The present invention circuit, the variable impedance element impedance of the minimum value or the resistance R of which one side or by appropriately selecting the value of both the third type resistor R _C and the variable impedance element up to a gain determined as the ratio of Z ₁ from the _C of Z ₁ Attenuation amount can be selected suitably.

This is actually the case to the gain control 2 with end etc. a two-stage configuration amplifier, one end and the resistor of the two-stage R _C, or second variable impedance elements to write because changes in the minimum value of Z ₁ is the distribution of the maximum attenuation of one stage and two-stage change However, the noise figure of the component amplifier can be improved.

FIG. 3 shows a specific embodiment of the present invention. In this example, the transistor Q ₃ is used instead of the variable impedance element Z ₁ . The operating bias power supply is supplied to the collector of transistor Q ₃ through the resistor R ₁ , and the base is grounded through the capacitor C ₁ to supply the gain control voltage V _AGC , and the connection point between the collector and the resistor R ₁ is connected to the capacitor C 3. It is connected to the collector of the transistor Q ₂ constituting a signal source via a _second.

This changes the gain control voltage V _AGC supplied to the base of transistor Q ₃ and makes the collector-emitter voltage V _CE a saturation region, so that the collector-base goes from the reverse bias state to the forward bias state. Impedance Z _cb changes from high impedance to low impedance.

Therefore, by connecting the low impedance at the frequency of use to the base of the transistor Q ₃ and mainly connecting the capacitor C ₁ for the side path, if the gain control signal voltage V _AGC is varied, the signal current i _O from the transistor Q ₂ is _changed to the transistor Q _3. The signal currents i ₂ and i ₁ are classified by the ratio of the impedance Z ₁ between the collector grounds and the resistance of the resistor R _C. Therefore, the signal current i ₂ is controlled by controlling the impedance between the collector grounds of the transistor Q ₃ by the gain control voltage V _AGC . Thus, a gain-controlled signal output voltage with V _O = i ₂ · R _L is obtained at the collector of transistor Q _{1 at} the output stage.

In this case, as it is also explained before noise source according to the distribution of the base resistance of the transistor Q ₁ r _bb 'will not have the gain for the output of the presence of the resistance R _C connected to the emitter of the transistor Q ₁ it does not appear at the output. For this reason, the deterioration of the noise figure characteristic is small with increasing attenuation amount.

Also by changing the capacitance value of the capacitor C _1, or of the resistor R _C to the maximum gain of the attenuation is determined by the ratio of resistors R _C and the variable impedance Z ₁ may be set to an appropriate value.

By the way, in the above-described embodiment, the capacitor C ₂ is interposed between the transistor Q ₂ and the variable impedance element Z ₁ to be alternatingly coupled, but a large gain control width can be obtained again by the direct current coupling.

4 shows an embodiment, in which the impedance between the collector ground of transistor Q ₃ changes in response to the variation of the gain control signal V _AGC , and the signal current i _O is classified into a resistor R _C and a variable impedance Z ₁ . The signal current i ₂ is varied by the change of the gain control signal V _AGC and the output voltage V _O = i ₂ · R _L is varied as described above.

On the other hand, the DC current of the transistor Q ₃ by the change of the gain control signal V _AGC is the collector emitter voltage V _CE of the transistor Q ₂ by the occurs a voltage drop in the variable resistor R _C is, it is variable, the transistor Q ₂ The amplification degree g _m changes. Therefore, it is possible to obtain a large gain variable width that obtains not only the gain change due to the classification effect described above, but also the gain change caused by the change in g _m of the transistor Q ₂ .

In this case, as shown in FIG. 5, by connecting resistors R ₂ and R ₃ to emitters of transistors Q ₂ and Q ₃ respectively, the voltage V _CE between the collector emitters of transistors Q ₂ and Q ₃ can be set separately. It is possible to arbitrarily change and set the starting point of the gain change caused by the change in gain and the amplification degree g _m , and the gain control sensitivity can be adjusted.

As shown in FIG. 6, the resistor γ is connected in series with the base of the transistor Q ₃ , and the resistance value of the resistor γ is selected as an appropriate value, so that the maximum attenuation of the gain change is made in accordance with the selection of the capacitance value of the side capacitor. Can be selected.

As the variable impedance element, not only the transistor but also the diode D as shown in FIG. 7 can be used as described above. In the case of using the diode D as described above, as shown in FIG. 8, by setting the resistor γ for setting the maximum attenuation amount in series with the diode D, the maximum attenuation amount of the gain control is set to an arbitrary value in accordance with the capacitance value selection of the capacitor C ₁ . There is a number.

As described above, according to the present invention, a gain control circuit can be obtained in which not only the noise index due to gain attenuation is deteriorated but also the maximum attenuation amount can be easily set.

Claims (1)

As described above and shown in the drawings, the transistor θ ₂ constituting the signal current source, the resistor R _C connected in series with the collector of the transistor, and the base ground connected with the emitter at the other end of the resistor Gain control consisting of a type transistor θ ₁ , a load impedance R _L connected in series with a collector of the base grounding transistor, and a variable impedance element Z ₁ connected in parallel with a transistor constituting the signal current source. Circuit.

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