JPS5848515A - Nonlinear amplifying circuit - Google Patents

Abstract

PURPOSE:To obtain a small gain for a low input signal and a large gain for high input signal, by controlling the amount of negative feedback with a nonlinear switching element. CONSTITUTION:Transistors(TRs) Q3, Q4 constitute a differential amplifying circuit and TRs Q1, Q2 form a current mirror circuit. A TRQ5 forms an emitter follower circuit. With the absence of input signals, voltages V1, V2 are set to turn off TRs Q6, Q7. When a signal of input level for the AC level of VBQ4 which satisfies V1+VBEQ7>VBO4>V2-VBEQ6 is inputted, the TRs Q6, Q7 turn off. Next, the signal of input level in which the AC level of the VBQ4 satisfies V1+ VBEQ7<VBEQ7 and V2-VBEQ6>VBQ4 is inputted, the TRQ7 turns on and one end of a resistor R3 is grounded as AC. Thus, in this amplifier, a small gain can be obtained for a low input signal and a high gain to a high input signal, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nonlinear amplifier circuit, and more particularly, it has a small gain for low input level signals and a large gain for high input level signals. The present invention provides a nonlinear amplifier circuit having the following characteristics.

FIG. 1 is a block diagram for explaining the basic principle of a normal negative feedback amplifier circuit. In this amplifier circuit, the gain of the active load type differential amplifier circuit of the main body is Mu0, and the transfer function in the negative feedback loop is G(s).

If the input signal source voltage is Vi and the output voltage is vO, then
If this G(!) is controlled to be switched depending on the magnitude of the input signal level, as shown in Figure 2, a nonlinear amplifier circuit suitable for extracting only the signal component from a signal containing noise components can be created. It is possible to configure

3 shows an embodiment of the nonlinear amplifier circuit of the present invention. npn) transistor Q3. Q4 constitutes a differential amplifier circuit, and is the input stage of this circuit, pnp +
”Transistor 9.Q2 constitutes a current mirror circuit,
This is the load for each of the above transistors Qs and Q4. R1 is the input resistance! is the input bias power supply. Transistor Q5 is a component of the output stage emitter follower circuit, R (Rs, Ik, cl are resistor and capacitance elements that determine the nonlinear gain, Q6., Q7 are switching transistors, V+, V2~ are It is a voltage source.

In FIG. 3, the base of the transistor Qs in the input stage is biased with
, set V2. Now, vBq4's AC Leheka V
+ + VBxq7) V! lQ4 > V2 Va
When a signal is input at an input level that satisfies xq6, the transistor φ+Q' is cut off, and the transfer function G(s) that determines the amount of negative feedback is determined by: Here, SC is the impedance component of capacitor C. Therefore, the gain of this negative feedback type amplifier circuit as a whole is Q.

Next K, VBQ4 (7) AC level is V+ + VB
xq7<VBQ4.

If a signal is input at an input level that satisfies V2-VBXQ6>VBQ4, one end of R5 will be grounded in an alternating current manner. Therefore, the gain can be made larger than the gain at low input level.

In other words, the nonlinear amplifier circuit of the present embodiment described above can have the human output characteristics as shown in FIG. 4, and exhibits great effectiveness in the signal processing circuit as described above.

In addition, in the embodiment circuit of FIG. 3, the transistor Qb
, Q7 is not limited to a bipolar transistor or a -ra transistor, but the same circuit function can be realized by replacing it with a nonlinear switching element such as a nine-FIT or a diode set to an appropriate bias condition.

Above, five examples of nonlinear amplifier circuits and their characteristics have been explained, but the present invention can also be applied even when the polarity of the transistors in the circuit as described above is changed between NPN structure and PNPIII structure. Similarly useful circuit configurations are possible.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the basic principle of a negative feedback amplifier circuit, Fig. 2 is a diagram showing an example of a signal processed by the circuit, and Fig. 3 is a block diagram showing the basic principle of a negative feedback amplifier circuit.
The figure is a circuit diagram of a nonlinear amplifier circuit according to an embodiment of the present invention, and FIG. 4 is a diagram showing input/output characteristics of the nonlinear amplifier circuit. Ql, Q2. Q7°−°°p n p) ”) 7 transistors, Q' + Q'. Q5.Q6... npn) transistors, R+・
...Input resistance, E...Input bias power supply, R2,, Rs, R4...Resistance, C1...
····capacity. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure 4viA Vn =75-

Claims (1)

[Claims] The emitter sides of the first and second transistors are connected to a common constant current source, a differential base voltage is biased between the first and second transistors, and the collector side of each of the first and second transistors is biased between the first and second transistors. A pair of active elements consisting of a current mirror circuit are connected as respective loads, and the collector signal of the second transistor is outputted through the emitter follower circuit, and this output is applied to the second transistor through a resistor. 4. A nonlinear amplifier circuit characterized in that it has a configuration in which feedback is provided and the amount of feedback can be controlled by a nonlinear switching element.