JPS63288506A - Clipping circuit for multi-stage amplifier circuit - Google Patents

Abstract

PURPOSE:To attain clipping effectively by a slight current consumption by forming a negative feedback loop of a differential amplifier circuit in response to the detected current in detecting it that an output current of an emitter follower amplifier circuit to be a current corresponding to a clipping level. CONSTITUTION:When an output voltage Vout goes positively and exceeds a clipping level comprising a constant voltage source V4 and a transistor(TR) Q11, since an output current of a diode D1 is fed to a current mirror circuit via the TR Q11 the moment the TR Q11 is turned on via the TR Q11, the current equal thereto is drawn from the output current of a TR Q4. Thus, the collector current of the TR Q4 is increased and the collector current of a TR Q3 constituting the current mirror is also increased. A TR Q10 is turned off and a base current of a TR Q5 is increased, then the collector current of the TR Q5 is decreased and the output voltage Vout is decreasing. That is, even when a slight collector current of the TR Q11 flows, since the collector current of the TR Q11 starts flowing, since negative feedback is applied and the output voltage Vout is clipped without almost using the collector current of the TR Q11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a clip circuit for a multistage amplifier circuit that limits the amplitude of an output signal of the multistage amplifier circuit.

(Prior Art) Generally, an amplifier circuit for an audio device or the like is provided with a clip circuit that limits the amplitude of an output signal so that an amplitude voltage exceeding an input tolerance value of a subsequent stage circuit is not output.

As this clip circuit, for example, one-stage amplification 5EPP
In the case of a one-stage amplifier circuit such as a single-ended push-pull (single-end push-pull) circuit, a method of applying a voltage clip using a voltage between the base and emitter of a transistor is often used.

By the way, if the oven loop gain of the one-stage amplifier circuit is insufficient, a multi-stage amplification circuit configuration is adopted, but this multi-stage nine-stage amplifier circuit usually uses the same method as the one-stage amplifier circuit, as shown in Figure 3. A clip circuit is provided. In FIG. 3, A is a differential amplifier circuit, B is an emitter follower amplifier circuit, C is an output circuit, and D is a clip circuit.

The differential amplifier circuit A includes a differential pair transistor Ql.

Q2, bias current source ■1, transistor Q3゜Q4
．． It consists of a current mirror circuit (active load) consisting of resistors R1 and R2, and transistors Q1. Q2
The input voltage Vln and output voltage v supplied to each base of
This is to amplify the difference between the output and the output.

The emitter follower amplifier circuit B is composed of a transistor Q5, diodes DI and D2, and a bias current source I2,
The emitter current of the transistor Q5 is increased or decreased according to the output current of the differential amplifier circuit A (collector current of the transistor Q1).

Output circuit C is 5EPP consisting of transistor Q8.07
By controlling the transistors QB and Q7 according to the emitter potential of the emitter follower amplifier circuit B and the level shift potential by the diodes Di and D2, the output current of the emitter follower amplifier circuit C is power amplified and the output voltage is This is to obtain v out.

The clip circuit is the transistor Q8. Q9, constant voltage source V
L, V2, and the transistor Q6 of the output circuit C.
Similarly to Q7, transistors Q8 and Q9 are push-pull connected, and each transistor QB.

Predetermined control voltages VL and V2 are applied to Q9, respectively, and transistor Q8 or Q9 is set to an on state according to the level shift potential by diode D1. In other words, when the emitter current of the emitter follower amplifier circuit B increases and the level shift potential exceeds the control voltage V1, the transistor Q9 turns on and draws in the emitter current, clipping the output voltage Vout so that it does not rise any further. multiply. Conversely, the level shift potential is the control voltage V
When the voltage drops below 2, the transistor Q8 turns on and draws the base current of the transistor Q5 of the emitter follower amplifier circuit B, thereby applying a clip to prevent the output voltage V out from falling any further.

That is, the above clip circuit is connected to the transistor Q8.
The voltage between the base and emitter of Q9 is VBE (Q8
), VBE(Q9), the output voltage V out
V 1 + V 13E (Q8) < Vout <
V 2 + VBE(Q9)...(1) When in the range, transistor Q8. Since Q9 is in the off state, it does not affect the amplifier circuit at all.

At this time, the amplifier circuit is equivalent to a normal circuit without a clip circuit. When the output voltage V out attempts to exceed the range expressed by equation (1), the clip circuit begins to limit the output voltage V out. In other words, when trying to exceed the (-) side, the output voltage Vout- is as follows: V out- = V l + V BE (Q8)
-(2), the voltage is fixed at the voltage at which the transistor Q8 is turned on, and does not fall below that voltage. (
+) side, the output voltage V out
+ is V out+ −V 2 + V BE (Q9)
−(3), so transistor Q9
It is fixed at the voltage at which the switch is turned on and will not rise above that voltage. Therefore, the amplitude of the output voltage is V out− and V
limited during out+.

However, in the clipping circuit of the conventional multi-stage amplifier circuit as described above, especially when limiting the amplitude of the output signal that swings to the (+) side, as shown by the arrow i in the figure, VCC? E
Current flows through the source, transistor Q5, diode D1, transistor Q9, and ground in this order, but since there is no element to limit the current in this path, an excessive amount of current is consumed.

Therefore, a large amount of power is consumed during the clipping operation.

(Problems to be Solved by the Invention) As described above, in the clip circuit of the conventional multi-stage amplifier circuit, an unnecessarily large current flows during the clip operation, resulting in large power consumption.

The present invention was made in order to solve the above-mentioned problems, and it is an object of the present invention to provide a clipping circuit for a multistage amplifier circuit that can optimally clip the amplitude of the output signal of the multistage amplifier circuit with a small amount of current consumption. purpose.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the clip circuit of the multi-stage amplifier circuit according to the present invention provides a first and a second output according to an input signal and an output signal. a differential amplifier circuit that differentially amplifies current in opposite directions; an emitter follower amplifier circuit that amplifies a first output current of the differential amplifier circuit; and an emitter follower amplifier circuit that amplifies the first output current of the differential amplifier circuit; The output current of the emitter follower amplifier circuit is used in a multistage amplifier circuit having an output circuit for obtaining a signal, and clips the output signal when the output signal exceeds a first or second level. 1. Current detecting means for detecting that the amount of current has reached a second level, and a negative current detecting means for limiting the second output current of the differential amplifier circuit according to the detected current value of the current detecting means. and current limiting means forming a feedback loop.

(Function) The clipping circuit of the multistage amplifier circuit with the above configuration operates when the output current of the emitter follower amplifier circuit reaches the first and second current amounts corresponding to the first and second levels of the output signal to be clipped. , a negative feedback loop works to limit the second output current of the differential amplifier circuit by multiplying this, so in the case where the first output tlsffi is limited, the amplitude of the output signal is different from the first or second output current. When this level is reached, the negative feedback loop is activated immediately, so no more current is consumed than necessary.

(Embodiment) An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 shows a configuration in which the present invention is applied to the multistage amplifier circuit shown in FIG. In FIG. 1, the same parts as in FIG. 3 are designated by the same reference numerals, and different parts will be described here.

That is, the clip circuit E used here connects the collector of an NPN transistor QIO to the collector of the transistor Ql of the differential amplifier circuit A, and
The emitter of IO is connected to the connection point of diodes Dl and D2, and also to the emitter of PNP transistor Qll. The collector of this transistor Qll is connected to the transistor Q12. Q13 is connected to the input terminal of the current mirror circuit (collector of transistor Q12), and the output terminal of this current mirror circuit (transistor Q
13) is connected to the collector of the transistor Q2 of the differential amplifier circuit A. Furthermore, each transistor Q
Each base of IO and Qll is connected to a constant voltage source V3. V4
Connect to the (+) terminal of the

The clipping circuit with this configuration has a clipping level of V out--V 3 + V 13E (QIO), similar to the circuit shown in FIG.
・” (4) V out+= V 4 +
VBE(Qll) - (5) is set to the value shown, and V3 + VBE(QIO) < Vout < V4
+VBE(Qll)...(6) If it is within the range, both transistors QIO and Qll are turned off and do not affect the output voltage V out.

Now, the output voltage V out swings to the (+) side, and the constant voltage source V
When the clip level due to transistor Q4 and transistor Qll is exceeded, the output current of diode DI is input to the current mirror circuit via transistor Qll at the moment transistor Qll is turned on, so that a current equivalent to this is input from the output current of transistor Q4. be drawn out. For this reason,
The collector current of transistor Q4 increases, and the collector current of transistor Q3 forming a current mirror with transistor Q4 also increases. At this time, the transistor QIO is off and the base current of the transistor Q5 increases, so the collector current of the transistor Q5 decreases.
As a result, the output voltage v out acts in a decreasing direction.

That is, when the transistor Qll is turned on at the time when the output voltage v out exceeds the (+) side clip level, negative feedback is applied to prevent the output voltage V out from rising any further. In this case, if even a small amount of the collector current of the transistor Qll begins to flow, negative feedback begins to occur, so that the output voltage V out can be clipped without consuming much of the collector current of the transistor Qll.

Similarly, when the transistor QIO is turned on at the time when the output voltage V out exceeds the (-) side clip level, negative feedback is applied to prevent the output voltage V out from falling any further. In this case, if even a small amount of the collector current of the transistor QIO begins to flow, negative feedback begins to occur, so that the output voltage V out can be clipped without consuming much of the collector current of the transistor QIO.

Therefore, if the clip circuit with the above configuration is used,
The amplitude of the output voltage can be effectively clipped with a small amount of current consumption.

FIG. 2 shows another embodiment, in which the same parts as in FIG. 1 are denoted by the same reference numerals. The amplifier circuit used here has a power supply voltage of positive and negative voltage terminals VCC.

-VEE, and the output voltage V out is at ground potential (O
It is designed so that it can swing around [Vl].

The resistor R3 is used to set the base potential of the transistor Q1.

For such an amplifier circuit, the clip circuit E' is a transistor Q that limits the (-) side amplitude of the output voltage v out.
Transistor Q 14. without returning the collector current of transistor Q 14. After the current is reversed by a current mirror circuit consisting of Q15, feedback is applied to the same point as the output point (collector of transistor Q13) of the current mirror circuit that limits the amplitude on the (+) side. A constant voltage source V
5. It is set for earth (0 [Vl) 71st place by VG.

That is, in the clip circuit with this configuration, the clip level is Vout---(V 5 , +VBE(QIO)
) = 17) V out+ −V B + V
BE(Qll)-(8) is set to the value shown, and its operation is completely (same) as the circuit in FIG.

As in this embodiment, there are no particular limitations on the current feedback means of the invention of the present application, as long as the current generated when clipping the output signal is fed back in the direction in which the current decreases. Clips can be applied effectively with a small amount of current consumption.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a clipping circuit for a multistage amplifier circuit that can optimally clip the amplitude of the output signal of the multistage amplifier circuit with a small amount of current consumption.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of a clip circuit of a multi-stage amplifier circuit according to the present invention, FIG. 2 is a circuit diagram showing another embodiment of the present invention, and FIG. 3 is a circuit diagram of a conventional multi-stage amplifier circuit. FIG. 2 is a circuit diagram showing the configuration of a clip circuit. A... Differential amplifier circuit, B... Emitter follower circuit, C... Output circuit, D, E, E''... Clip circuit.

Claims (1)

[Claims] A differential amplifier circuit that differentially amplifies first and second output currents in opposite directions according to an input signal and an output signal, and an emitter follower amplifier circuit that amplifies the first output current of the differential amplifier circuit. and an output circuit that obtains the output signal based on the output current of the emitter follower amplifier circuit, and the output signal is transmitted to the first and second
In a clipping circuit of a multi-stage amplifier circuit that clips the output signal when the output signal exceeds a level of A clip for a multi-stage amplifier circuit comprising a detection means and a current limiting means forming a negative feedback loop to limit a second output current of the differential amplifier circuit according to a current value detected by the current detection means. circuit.