JP2781850B2 - Variable gain amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a current shunt type variable gain amplifier circuit, which sets a variable gain amplifier circuit capable of performing a level shift together.

[Conventional technology]

As a variable gain amplifier circuit, a current split type shown in FIG. 3 is known. This circuit has an amplifier circuit 10 and a differential voltage generation circuit 30. The differential voltage generating circuit 30 includes a diode 31 (32), a transistor 33 (34) and a resistor 35 (3
6) a series circuit with a constant current source circuit 37 (38) composed of a series circuit and the like, and a diode 31 (32) and a constant current source circuit 37
The potential at the connection point with (38) is output to the bases of the transistors 14, 16 (13, 15) of the amplifier circuit 10.

The resistor 36 is a variable resistor, and the output potentials of the diodes 31 and 32 differ according to the difference between the resistance value of the resistor 36 and the resistance value of the resistor 35. , 14 or 15, 16 gates.

The amplifier circuit 10 includes a load resistor 11 (12) and a transistor 13
The series circuit of (15) and the transistor 14 (16) are connected in parallel, and this parallel circuit, the transistor 17 (18), and the constant current source circuit 19 (20) are connected in series.
A resistor 21 is interposed between the emitters of the transistors 7 and 18.
Positive and negative inputs are applied to the bases 8 through resistors 22 and 23, respectively, and connection points between the resistors 12 and 11 and the transistors 15 and 13 are used as positive and negative output terminals.

[Problems to be solved by the invention]

In the above circuit, amplification is performed with a gain determined by the value of the resistor 36. When shifting the level of the amplified output, it is necessary to provide a shift circuit at the subsequent stage of this circuit. Conversely, when an input signal is shifted and then amplified, it is necessary to provide a shift circuit before the circuit.

At this time, the level shift amount and the amplification gain had to be separately adjusted.

An object of the present invention is to provide a variable gain amplifying circuit which can perform such a shift and can simultaneously set the shift amount and the amplification gain.

[Means for solving the problem]

A variable gain amplifier circuit according to the present invention includes two series circuits each including a diode and a first constant current source, and a current capable of continuously changing a current flowing through the at least one series circuit. A gain-variable differential voltage generating circuit having a variable circuit;
And a second differential transistor pair circuit using each of the transistors of the first differential transistor pair circuit as a constant current source transistor. Applying the gain-variable differential voltage generated by the circuit to the second differential transistor pair circuit;
In a variable gain amplifier circuit for setting an amplification gain by changing an output current shunt ratio of each transistor in the second differential transistor pair circuit, the variable current amplifier circuit is connected to one input terminal of the first differential transistor pair circuit, A second constant current source whose output current is continuously variable by a variable circuit;
By changing the output current of the second constant current source, the DC voltage level of the signal input to the input terminal is shifted, and the DC voltage level is reduced or increased in accordance with the increase or decrease of the amplification gain. Wherein the output voltage level of the signal is shifted.

[Action]

The input signal input to the one input terminal is shifted by a value determined according to the supply current of the second constant current source,
It will be amplified in that state.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings showing the embodiments.

FIG. 1 is a circuit diagram showing a first embodiment of the variable gain amplifier circuit of the present invention. The amplification circuit 10 and the differential voltage generation circuit 30 are connected between the power supply line of the potential V _CC and the ground line. The differential voltage generating circuit 30 is the same as that of FIG. 3, but the description of the previously omitted portions is as follows.

That is, a series circuit of the constant current source circuit 39, the transistor 40, and the resistor 41 is connected between the power supply line and the ground line. The base and the collector of the transistor 40 are collectively connected, and this is connected to the bases of the transistors 33 and 34. is there. Also, a series circuit 37 (38) of a transistor 33 (34) and a resistor 35 (36)
The series circuit of the diode 31 (32)
The anode side of 2) is connected to a power supply line via a bias circuit 38.

The anode potentials of diodes 31 and 32 are set to V _D , diode 3
Let the voltage drops of ₁ , 32 be v ₀ , v ₁ , the currents flowing through these diodes be I ₀ , I ₁ , and the resistance values of resistors 35, 36 be R ₀ , R ₁ . The current flowing through the constant current source circuit 39 is represented by I _S , and the resistance of the resistor 41 is represented by R _S.

On the other hand, the configuration of the amplifier circuit 10 is the same as that shown in FIG. That is, the amplifier circuit section 10 connects a series circuit of the load resistor 11 (12) and the transistor 13 (15) and the transistor 14 (16) in parallel, and the parallel circuit and the transistor 17 (18)
And the constant current source circuit 19 (20) are connected in series. A resistor 21 is interposed between the emitters of the transistors 17 and 18, and the bases of the transistors 17 and 18 are connected via resistors 22 and 23, respectively. To provide positive and negative inputs, resistors 12, 11 and transistors 15, 13 respectively.
The connection points with each become positive and negative output terminals. The values of resistors 11 and 12 are both R _C , and the values of resistors 22 and 23 are R ₂ ,
And R _3. The current values flowing through the transistors 13, 14, 15, 16 are I _2a , I _2b , I _3a , I _{3b, respectively,} and the supply currents of the constant current sources 19, 20 are I ₂ , I ₃ . The potentials of the input signals to the resistors 22 and 23 are set to V ₂ and V _{3, respectively,} and a differential voltage for varying the gain is applied between the base of the transistor 13 (15) and the base of the transistor 14 (16). the that voltage and Δ _v.

Thus, the feature of the circuit of the present invention is that the transistor 17 and the differential transistor pair input circuit (first differential transistor pair circuit) are equal to each other. Source). In the embodiment of FIG. 1, the collectors of the transistors 24 and 25 (second constant current source) are connected together to the base of the transistor 17, and the emitters are connected to the transistors 33 and 34 (first constant current source), respectively. The base is connected to a constant current source circuit 39 together with the bases of the transistors 33, 34, and 40. Here, the resistors 3 that constitute the other constant current source circuits 37 and 38
A constant current source circuit is constituted by the transistors 24 and 25 by using 5, 36 (resistor 36; current variable circuit) and the like, and the constant current source circuits 37 and 38 and the current mirror circuit are constituted. I have.

Next, the operation of the above circuit will be described. If now it is assumed transistors 40,33,34,24,25 are equal, the current also each I ₀ flowing through the transistors 24 and 25, because the _{I 1 V BES + I S ·} R S = V BE0 + 2I 0 · R 0 = V _BE1 + 2I ₁ · R ₁ … (1) where V _BES : Base-emitter voltage of transistor 40 V _BE0 : Base-emitter voltage of transistors 33 and 24 V _BE1 : Base-emitter voltage of transistors 34 and 25 However, q: charge amount 1.6 × 10 ⁻¹⁹ (C) k: Boltzmann constant 1.38 × 10 ⁻²³ (J / K) T: currents I ₀ , I ₁ flowing through diodes 31 and 32 because the absolute temperature is 300 (K) Between Is established.

That is, the current I flowing through the diodes 31 and 32 due to R ₀ and R _1
0 and I ₁ are determined.

However, in order to set I ₀ = I ₁ , since V _BE0 = V _BES, it is _sufficient to set R ₀ = R _S / 2 (6). Therefore Becomes

Thus, the differential voltage _ΔV is However, Ir: because the reverse saturation current of the diodes 31 and 32 (5) using the equation when _{Δ V = 2 (I 0 R} 0 -I 1 R 1) ... (9) next, delta _V is I _0, It can be seen that it is determined by I ₁ or the resistance values R ₀ and R ₁ of the resistors 35 and 36.

This differential voltage _ΔV is the differential transistor pair 13 and 14, or 15
And the shunt ratio of the current at 16 are determined. That is Eliminating _ΔV using equation (8) Becomes The gain of the amplifier circuit section 10 is determined by the shunt by the differential transistor pairs 13 and 14, and 15 and 16, and the variation K is given by equation (11). Becomes In short, the gain is determined by R ₀ and R _1. On the other hand, the gain can be set to a predetermined value by making the resistor 36 variable.

Next, looking at the voltage shift according to the gist of the present invention,
Since the current I ₀ + I ₁ of the constant current circuit flows through the input terminal of the voltage V ₂ , the base voltage of the transistor 17 shifts (decreases) by Δv _i = R ₂ (I ₀ + I ₁ ) (13). The current of diodes 31 and 32
The gain G when I ₀ and I ₁ is However G _0: maximum shift amount in the output and give a voltage shift of Delta] v _i in the case of the gain current gain G (decrease amount) [Delta] V ₀ of the amplifier circuit 10 Thus it is made possible a shift by changing the I ₁ by adjusting the R ₁ by changing the gain G, also contrary to the change in gain G [Delta] V _0.

Although the transistor 24 is provided on the resistor 35 side in the above embodiment, the transistor 24 can be omitted.

FIG. 2 shows another embodiment of the present invention. In this embodiment, a constant current source circuit comprising a series circuit of a transistor 27 and a resistor 28 is provided between the base of the transistor 17 and the ground line. The base of the transistor 27 is a constant current source circuit 39
It is connected to. In the case of this circuit, the input level can be shifted by a fixed amount by the constant current circuit.

〔The invention's effect〕

In the case of the present invention as described above, the shift amount of the DC voltage level due to the current flowing through the constant current source is continuously variable, and the change in the amplification gain and the change in the shift amount of the DC voltage level are incompatible. Therefore, the shift amount of the DC voltage level can be arbitrarily selected, and the output signal level does not become excessive even when the gain is increased, and the dynamic range of the output signal can be widened. The present invention has excellent effects, for example, the elements of the constant current source itself can be shared and the number of elements used can be reduced.

[Brief description of the drawings]

1 and 2 are circuit diagrams of a variable gain amplifier circuit of the present invention, and FIG. 3 is a circuit diagram of a conventional variable gain amplifier circuit. 10 ... amplifying circuit, 17,18 ... transistor 24,25,27 ... transistor, 28 ... resistor 30 ... differential voltage generating circuit, 31,32 ... diode 37,38 ... constant current source circuit. Indicates the same or corresponding parts.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-61-152109 (JP, A) JP-A-57-127311 (JP, A) JP-A-56-35514 (JP, A) JP-A-62 117404 (JP, A) Japanese Utility Model Showa 57-143711 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) H03G 3/10

Claims (1)

(57) [Claims] 1. A gain comprising a series circuit comprising a diode and a first constant current source, and a current variable circuit capable of continuously changing a current flowing through the at least one series circuit. A variable differential voltage generating circuit, a first differential transistor pair circuit to which a signal to be amplified is input, and two transistors each having a constant current source transistor as each transistor of the first differential transistor pair circuit. A second differential transistor pair circuit, wherein the variable gain differential voltage generated by the variable gain differential voltage generating circuit is supplied to the second differential transistor pair circuit, and the second differential transistor pair circuit is provided. In the variable gain amplifier circuit for setting an amplification gain by changing an output current shunt ratio of each transistor in the first embodiment, the variable gain amplifier circuit is connected to one input terminal of a first differential transistor pair circuit, A second constant current source whose output current is continuously variable by a transformer circuit; and by changing an output current of the second constant current source, a DC voltage level of the signal input to the input terminal is changed. A variable gain amplifier circuit for shifting the DC voltage level according to the increase and decrease of the amplification gain, and for shifting the output voltage level of the signal.