JPH0349207B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical field to which the invention pertains) The present invention relates to a bias circuit, and particularly to a DC bias circuit for a plurality of AC voltage amplifiers suitable for integration into an integrated circuit.

(Prior Art) FIG. 1 shows a conventionally well-known DC bias circuit. To explain this, the voltage at the current terminal 2 is divided by the resistors R ₁ and R ₂ , and the voltage at the current terminal 2 is divided by the resistors R ₁ and R _{2 .}
A resistor is connected between the connection point 4 of the amplifier 7 and the input terminal 1 of the amplifier 7.
_R3 is connected to provide a DC bias to the input terminal 1 of the amplifier 7. The same can be said about amplifier 9. The AC input signal applied to the signal input terminal 6 is applied to the input terminal 1 of the voltage amplifier ₇ through the DC blocking capacitor C2. Here, the leakage amount v ₄ of the AC input signal to the connection point 4 of the resistors R ₁ and R ₂ when the AC human input signal is applied is as follows (2)
It is generally governed by the capacitance value of the capacitor _C1 , and is set to a value where the influence on other amplifiers 9 can be ignored.

Z ₄ = 1/2πfC ₁ +1/R ₁ +1/R ₂ ...(1) v ₄ =Z ₄ /R ₃ +Z ₄ ×v _i ...(2) Here, π is pi and f is the input signal frequency,
C ₁ represents a capacitance value, Z ₄ represents an impedance viewed from the terminal 4 to the ground side, and v ₁ represents an AC input signal voltage value. However, it is assumed that the impedance when looking at the amplifier 9 is so large that it can be ignored. In fact, to give an example, f = 1KHz, C ₁ = 47μF, R ₁ = R ₂ =
At 10KΩ, Z ₄ = 33.9Ω, and R ₃ = 50KΩ,
v ₄ ≒6.8×10 ^-5 v _i .

By the way, in integrated circuits, the increase in the number of external connection terminals and the increase in the number of external additional parts (single components that are connected to the external connection terminals of the integrated circuit and form a circuit together with the integrated circuit) are major drawbacks in terms of price and shape. It is. When the circuit in FIG. 1 is integrated, the area inside the broken line 5 is integrated.
1, 2, 3, 4, 8, 10, and 11 are external connection terminals, and capacitors C ₁ , C ₂ , and C ₃ are external additional components. In other words, there are seven external connection terminals and three external additional parts.

Next, FIG. 2 will be described as another conventional example.
In FIG. 2, parts corresponding to those in FIG. 1 are designated by the same numbers, and their explanation will be omitted. The only difference from Figure 1 is that transistors Q ₁ and Q ₂ with collector bases shorted are connected in series to resistors R ₁ and R ₂ that are connected in series between power supply terminal 2 and ground terminal 3. , is equivalent to that explained in FIG. 1 above.
When the circuit shown in FIG. 2 is integrated, the portion inside the broken line 5 is integrated. As in Figure 1, 1,
2, 3, 4, 8, 10 and 11 are external connection terminals, and capacitors C ₁ , C ₂ and C ₃ are external additional components. In other words, there are seven external connection terminals and three external additional parts.

(Object of the Invention) An object of the present invention is to provide a DC bias circuit that commonly supplies a DC bias of 1/2 of the power supply voltage to a plurality of voltage amplifiers and has little mutual influence of AC input signals on each other. There is a particular thing.

(Structure of the Invention) The bias circuit of the present invention divides the voltage of a DC power supply with a plurality of resistors and supplies DC bias from the DC bias output terminal to the input terminals of the plurality of AC voltage amplifiers via the respective series resistors. The bias circuit includes a current mirror circuit of one conductivity type having an output transistor whose emitter is connected to one end of the DC power supply via an emitter resistor, and a collector current of the output transistor is input to the collector, and the emitter is connected to one end of the DC power supply. A reverse conduction type current transistor having an input transistor connected to the other end, an output transistor having an emitter connected to the other end of the DC power supply and a collector connected to the DC bias output end and forming one of the resistors. a mirror circuit, the base of which is connected to the emitter of the output transistor of the one-conductivity type current mirror circuit, the collector of which is connected to the one end of the DC power supply, and the emitter of which is connected to the DC bias output end of the resistor; and an emitter follower circuit constituting the other.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 3 is a circuit diagram showing one embodiment of the present invention. Note that parts corresponding to those in FIGS. 1 and 2 are designated by the same numbers, and their explanations will be omitted.

3, the difference from the conventional example shown in FIG. 2 is that PNP transistors Q 3 and Q ₅ are connected between the DC bias output terminals of voltage amplifiers 7 and 9 and _the common connection point of transistors Q ₁ and Q ₂ . consists of
A bias supply circuit consisting of a PNP type current mirror circuit and an emitter follower of NPN transistor _Q4 and PNP transistor _Q6 is provided.

Here, the NPN transistors Q2 and Q4 constitute an NPN type current mirror circuit having emitter resistors R2 and R5.

In Figure 3, the voltage at power supply terminal 2 is
It is divided by R ₁ , R ₂ and diodes Q ₁ , Q ₂ , and from the dividing point via the emitter follower circuit of transistors Q ₄ and Q ₆ , a voltage amplifier 7 is connected to the intersection between the emitter of transistor Q ₆ and the collector of transistor Q ₅ . The input terminal 1 of the voltage amplifier 7 is connected to the input terminal 1 of the voltage amplifier 7 via a resistor _R3 , and a DC bias is applied to the input terminal 1 of the voltage amplifier 7. The same can be said about voltage amplifier 9.

The AC input signal given to the signal input terminal 6 is
Voltage amplifier 7 via DC blocking capacitor C ₂
is applied to input terminal 1 of . Here, when an AC input signal is applied, the leakage of the AC input signal to the intersection (point a) with the collector of the transistor Q ₅ , the emitter of the transistor Q ₆ , and the resistors R ₃ and R ₄ (point _a ) is as follows ( 4) Given by Eq.

1/Z ₄ '=1/Z _Q5 +1/r _eQ6 +R ₁ ×R ₂ ×R ₅ /hFE
EQ6×{R ₁ ×R ₂ +hFEQ4×R ₅ (R ₁ +R ₂ )}……(3) v ₄ ′=Z ₄ ′/R ₃ +Z ₄ ′×v _i ……(4) Here, Z _Q5 is the output impedance of transistor _Q5 , r _eQ6 is the emitter resistance of transistor _Q6 ,
hFEQ4 and hFEQ6 are the current amplification factors of transistors _Q4 and _Q6 , _Z4 ' is the impedance seen from the emitter of transistor _Q4 to the ground side, and v _i is the AC input signal voltage value. Generally Z _Q5 is around 100KΩ,
Since hFEQ4 and hFEQ6 are around 100 and r _eQ6 is around several Ω, Z ₄ ' is the emitter resistance of transistor Q ₆ r _eQ6
ruled by. Therefore, the resistance value of R ₃ is set large so that the influence of the leakage portion v ₄ ' of the AC input signal on the other amplifiers 9 can be ignored. The same applies to resistor _R4 . In fact, to give an example, Z ₄ ′≒3.1
Ω, R ₃ =50KΩ, v ₄ ′≒6.25×10 ⁻⁵ v _i , and the leakage v ₄ ′ can be easily made smaller than in the conventional circuit.

Here, if the values of resistors R1, R2, and R5 are made the same, the collector current of the output transistor Q4 of the NPN type current mirror circuit will be the same as the emitter DC current of transistor Q2, and will be the same as the DC bias current of each transistor Q3 to Q6. becomes.

Therefore, even if the power supply voltage supplied between power supply terminals 2 and 3 fluctuates, the DC resistance of transistors Q5 and Q6, which form two resistors, will be the same, and the voltage at the DC bias output terminal will always be 1 of the power supply voltage. /2 has the effect of stabilizing it.

Next, FIG. 4 shows a circuit diagram of another embodiment. Fourth
The difference between this figure and FIG. 3 is that the PNP transistor is replaced with an NPN transistor, and the NPN transistor is replaced with a PNP transistor, and the circuit operation status is the same as that shown in FIG. 3.

Here, when the present invention is integrated into an integrated circuit, the third
As shown in Figures 1 and 4, the area inside the broken line 5 is integrated, and the integrated circuit has one external connection terminal and one external additional component reduced compared to the conventional example shown in Figures 1 and 2. It is possible to provide.

(Effects of the Invention) As explained in detail above, according to the present invention,
As a common bias circuit for multiple AC voltage amplifiers, it has an emitter follower circuit that includes two NPN type and PNP type current mirror circuits, so the DC bias output terminal always maintains the value where the power supply voltage is divided into two. Moreover, it is possible to provide a DC bias circuit that is less influenced by AC input signals on each other.

[Brief explanation of drawings]

1 and 2 are conventional circuit diagrams, FIG. 3 is a circuit diagram of one embodiment of the present invention, and FIG. 4 is a circuit diagram of another embodiment of the present invention. In the figure, 1, 6, 11, 12... input terminal, 2... power supply terminal, 3... ground terminal, 4... bias terminal, 5... integrated circuit part, 7, 9...
Voltage amplifier, 8, 10... Output terminal, R ₁ to R ₅ ...
...Resistance, C ₁ to C ₃ ... Capacitor, Q ₁ , Q ₂ , Q ₄ ,
Q ₁₀ , Q ₁₁ , Q ₁₂ ...NPN transistor, Q ₃ , Q ₅ ,
Q ₆ , Q ₇ , Q ₈ , Q ₉ ...PNP transistors.

Claims (1)

[Claims] 1. In a bias circuit that divides the voltage of a DC power supply with multiple resistors and supplies DC bias from the DC bias output terminal to the input terminals of multiple AC voltage amplifiers via the respective series resistors, a current mirror circuit of one conductivity type having an output transistor connected to one end of the DC power supply, and an input transistor having a collector inputting the collector current of the output transistor and an emitter connected to the other end of the DC power supply; A current mirror circuit of opposite conductivity type constitutes one of the resistors, and an output transistor whose emitter is connected to the other end of the DC power source and whose collector is connected to the DC bias output terminal constitutes one of the resistors; an emitter follower circuit connected to the emitter of the output transistor of the current mirror circuit, having a collector connected to the one end of the DC power source, and having an emitter connected to the DC bias output end to constitute the other resistor. Features a bias circuit.