JPH0379882B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier circuit, and more particularly to a multistage amplifier circuit having a plurality of amplification stages.

A general multi-stage amplifier circuit consisting of a plurality of amplifier stages is shown in FIG. 1, and the input signal is transmitted through differentially connected transistors Q ₁ and Q ₂ , a constant current source I ₁ and an active load current mirror transistor Q _{3 .} , _Q4 , which is a current amplification stage, performs current conversion. Note that R ₁ is an input resistance, and R ₂ and R ₃ are emitter resistances of current mirror transistors Q ₃ and Q ₄ .

This current output is voltage-converted and amplified by the amplification transistor _Q5 , which is a voltage amplification stage, and is output from its collector. This output is connected to a complementary pair of transistors in the next amplification stage.
This is the base drive voltage for Q ₆ and Q ₇ . Note that 10 is a base bias generation source for the transistors Q ₆ and Q ₇ and is composed of, for example, a diode. A constant current source _I2 is provided to supply operating current to the bias source 10, and _E1 is a transistor.
This determines the emitter voltage of _Q5 .

Both emitters of transistors Q ₆ and Q ₇ are resistors R ₄ ,
They are connected to the circuit output OUT via _R5 , and push-pull drive a common load (not shown) with low impedance. A capacitive element C is provided between the base and collector of the transistor Q ₅ for phase compensation, and a negative feedback circuit consisting of resistors R ₆ and R ₇ connects the circuit output with the transistor Q ₂ of the differential amplifier. It has the function of improving the circuit characteristics and maintaining the DC level at the circuit output point at zero potential.

In such a _circuit configuration as _{shown in FIG .} This will be referred to as the second amplification stage.

In the above configuration, in order to increase the utilization rate of the power supply voltage ±V ₁ , the voltage drop in the resistors R ₂ and R ₃ , the voltage loss in the constant current source I ₂ , and the reference bias voltage E ₁
It is normal to set it to small. In this case, the first
The transistor which is the output active element of the amplifier stage 1 of
The collector potential of Q ₅ swings from a potential E ₁ lower than the power supply voltage +V ₁ to a potential higher than the power supply voltage -V ₁ by the voltage loss of the current source I ₂ , so the withstand voltage of the transistor Q ₅ is Approximately 2×V ₁ is required. Therefore, high-voltage technology is required to integrate the first amplification stage 1 including the transistors Q ₁ to _{Q 5} and the current source I ₂ , but since there is a limit to increasing the voltage resistance, the conventional so-called This results in significantly inferior performance compared to a configuration using discrete components.

An object of the present invention is to provide a multi-stage amplifier circuit that does not require a high breakdown voltage and uses low breakdown voltage elements to facilitate circuit integration.

In order to achieve the above object, the multi-stage amplifier circuit of the present invention interposes a relay circuit constituted by a current mirror circuit between the front-stage push-pull amplifier circuit and the rear-stage push-pull amplifier circuit, and arranges both amplifier circuits separately. is characterized in that it is driven at a relatively low voltage, and the subsequent stage amplifier circuit is driven at a higher voltage than this.

The present invention will be explained below based on the drawings.

FIG. 2 is a circuit diagram of an embodiment of the present invention.
Parts equivalent to those in the figures are designated by the same reference numerals. That is, a current transfer means 3 consisting of a current mirror circuit is provided between the input and output of the first and second amplification stages 1 and 2, and the operating voltage sources of both the amplification stages 1 and 2 are separated from each other. To be more specific, the first
The collector output current of the PNP transistor _Q5 , which is the output amplification element of the amplifier stage 1, is converted into the collector output current of the transistor _Q9 by the first current mirror circuit consisting of the NPN transistors _Q8 and _Q9 . The collector output current of Q ₉ is transferred to a second transistor consisting of PNP transistors Q ₁₀ and Q ₁₁ .
Transistor Q ₁₁ by the current mirror circuit of
The current is converted to the collector output current.
Note that the resistors R ₈ to _{R 11} are the emitter resistances of the current mirror transistors Q ₈ to _{Q 11} , and when the mirror ratio (current transfer ratio) is 1, R ₈ = R ₉ , R ₁₀
= R ₁₁ . The collector output of the output transistor Q ₁₁ of the second current mirror circuit is used as the input drive current of the second amplification stage, and this collector output point connects the base of the output amplification element Q ₆ and the bias circuit 10. It is connected to a connection point.

By doing this, the operating voltage sources of the first and second amplification stages can be separated from each other, and the operating voltage sources of the first and second amplification stages can be separated from each other.
The amplification stage can be operated at a voltage ±V _{2 lower than the operating voltage ±V 1 of} the second amplification stage which is the output stage. Therefore, the withstand voltage of each element may be small, and integration into an integrated circuit becomes extremely easy. Specifically, the front stage section can be made into an IC with the dashed line α-α' in the figure as a boundary, and the rear stage section can be constructed from discrete components with high voltage resistance.

In the example shown in Figure 2, the input side transistor _Q8 of the first current mirror circuit is a low voltage element and can be integrated into an IC, but the output side transistor _Q9 needs to be a high voltage element and is a discrete component. . Therefore, the difference in V _BE (base-emitter voltage) between transistors _Q8 and _Q9 , the difference in value between resistors _R8 and _R9 ,
Furthermore, due to differences in temperature characteristics of these elements, the mirror ratio does not match the designed value, and the open loop gain and frequency characteristics of the amplifier circuit change.

To avoid this drawback, a circuit according to another embodiment of the invention is obtained, as shown in FIG. In FIG. 3, the same parts as in FIGS. 1 and 2 are given the same reference numerals, and the output of the first current mirror circuit consisting of transistors Q ₈ and Q ₉ and the transistors Q ₁₀ and
A common base type NPN transistor _Q12 is inserted in cascode connection between the input of the second current mirror circuit consisting of _Q11 . By doing this, transistors Q ₉ and Q ₁₂ perform a so-called cascode operation, and the collector potential of transistor Q ₉ is clamped to a substantially constant value (zero volts), and compared to the case shown in FIG _. It can be made into a low breakdown voltage element. Therefore, transistor Q ₉ is also on the same chip as transistor Q ₈ .
Since it can be implemented as an IC, the characteristics can be made uniform and the mirror ratio of the first current mirror circuit can be set as designed, leading to stabilization of the circuit.

In addition, in the circuits of Figures 2 and 3, in order to obtain the same frequency characteristics as the circuit of Figure 1, the value of the phase compensation capacitor C ₁ must be selected larger than that of the circuit of Figure 1. I have to do it, but the second and third
By connecting a capacitor _C1 between the base of transistor _Q5 and the base of transistor _Q6 in the circuit shown in the figure, the same frequency characteristics can be obtained with the same capacitance as in the circuit shown in FIG. Further, a capacitor _C1 may be provided between the base of the transistor _Q5 and the circuit output OUT.

FIG. 4 is a circuit diagram of another embodiment of the present invention,
Components equivalent to those in FIGS. 1 to 3 are designated by the same reference numerals. To describe only the parts that are different from the above examples, the input differential amplifier stage of the first amplification stage 1 is composed of FETs (field effect transistors) Q ₁ and Q ₂ , and each transistor Q ₁ , Q ₂ and Transistors Q ₁₃ and Q ₁₄ are connected in cascode, forming a cascode amplifier type. In addition, resistance R ₁₉
The base potentials of the transistors Q ₁₃ and Q ₄ are kept constant by the current sources I ₁ and I ₃ , and both transistors are operated in a base-grounded type. The load of the differential amplifier is a resistive load formed by resistors R ₁₃ and R ₁₄ , and a resistor R ₁₇ and a capacitor C ₂ are connected in series between the two loads.

Outputs derived from collector loads R ₁₃ and R ₄ are input to the second differential amplifier. This amplifier consists of differential transistors Q ₁₅ , Q ₁₆ , a current source I ₄ , and load resistors R ₁₅ , R ₁₆ , and the base input of transistor Q ₅ is taken out from both ends of resistor R ₁₆ . A cascode amplifier is configured by transistor _Q5 and transistor _Q18 , and the characteristics are improved. Note that _E2 is the base bias voltage source of transistor _Q18 . A phase compensation capacitor _C1 is inserted between the base of the transistor _Q5 and the collector of the transistor _Q18 . The collector output of this transistor _Q18 is
The current becomes the input current of the first current mirror circuit composed of Q ₈ and Q ₉ and is transferred to the next stage amplifying section 2. Thereafter, the configuration is the same as that of the circuit example shown in FIG. 3, and the explanation thereof will be omitted.

This example also has the advantage that the first voltage amplification stage 1 and the first current mirror circuit can be implemented as an IC on the same chip.

As explained above, the multistage amplifier circuit of the present invention has
In a multi-stage amplifier circuit consisting of a front-stage amplifier circuit and a rear-stage push-pull amplifier circuit, a current mirror circuit is inserted between both amplifier circuits, and both amplifier circuits are arranged separately, and a low power supply voltage is supplied to the front-stage amplifier circuit, while the latter stage Since the amplifier circuit is configured to supply a higher power supply voltage than this, the pre-amplifier section can be operated with a low power supply, so it can be configured with low-voltage elements, making it extremely easy to integrate into an IC. Become. Moreover,
The above-mentioned current mirror circuit, which relays the output of the front-stage amplifier circuit to the rear-stage amplifier circuit, has the advantage that it does not generate distortion in signal transmission and does not deteriorate the S/N or frequency characteristics of the entire multi-stage amplifier circuit. Another advantage is that it can be integrated into an IC together with the amplifier circuit. In addition, the maximum output of the entire amplifier circuit is determined by the circuits connected to the subsequent stage and their power supply voltages, so the front stage can be used for a wide range of amplifiers, from low output amplifiers to medium and small output amplifiers, providing versatility. will have.

In addition, a part of the bipolar element in the above is
It can be replaced with other active elements such as FET elements.

[Brief explanation of drawings]

Figure 1 shows an example of a conventional amplifier circuit; Figure 2 shows an example of a conventional amplifier circuit;
3 and 4 are circuit diagrams showing embodiments of the present invention, respectively. Explanation of symbols of main parts, 1...first amplification stage,
2... Second amplification stage, 3... Current transfer circuit, Q ₅
...Voltage amplification transistors, Q ₆ , Q ₇ ... Power amplification transistors, Q ₈ , Q ₉ , Q ₁₀ , Q ₁₁ ... Current mirror transistors.

Claims (1)

[Scope of Claims] 1. A multi-stage amplifier circuit including a front-stage transistor amplifier circuit and a rear-stage push-pull transistor amplifier circuit, the amplifier circuit being interposed between the front-stage transistor amplifier circuit and the rear-stage push-pull transistor amplifier circuit. relay means for relaying the output of the front-stage transistor amplifier circuit to the input of the rear-stage push-pull transistor amplifier circuit; and a power supply means for supplying a high power supply voltage, and the relay means includes a first current mirror circuit receiving the output current of the front-stage transistor amplifier circuit, and a power supply means for receiving the output current of the first current mirror circuit. a second current mirror circuit that supplies an output current corresponding to this to the input of the rear-stage push-pull transistor amplifier circuit, and wherein at least the front-stage transistor amplifier circuit is integrated. . 2. The multi-stage amplifier circuit according to claim 1, wherein the first-stage transistor amplifier circuit is a voltage amplifier circuit, and the second-stage push-pull transistor amplifier circuit is a power amplifier circuit. 3. The multistage circuit according to claim 1 or 2, wherein the input current path of the second current mirror circuit includes a transistor whose base is grounded to clamp the input current path to a low potential. Amplification circuit.