JPS5910627Y2 - Absolute value detection circuit - Google Patents

Description

[Detailed description of the invention] This invention relates to an absolute value detection circuit that detects the absolute value of an AC input signal, and more specifically, it is a full-wave rectifier circuit using a combinational circuit and the output of the combinational circuit. This invention relates to an absolute value detection circuit that eliminates crossover distortion due to the base-emitter voltage of the transistor and reduces the dead band for input by negatively feeding a portion of the input circuit to the input terminal of the input circuit of the full-wave rectifier circuit.

As an absolute value detection circuit using a full-wave rectifier circuit, a circuit that combines a diode and a capacitor constitutes a complementary push-pull circuit, in which the phase of the output of one element is inverted and taken out along with the output of the other element. There is a circuit that does this.

However, in the former case, the output rises slowly because there are circuit elements that include time constant elements in the circuit, making it unsuitable for applications that need to detect the instantaneous absolute value of the input AC signal, such as a peak meter. However, there is also the drawback that the frequency characteristics deteriorate at high frequencies.

In the latter case, the former problem can be solved, but the linearity is poor due to cross-over distortion caused by the base-emitter voltage of the transistor, and a dead zone occurs especially for small inputs below the above-mentioned voltage.

This idea was devised in view of the above points, and its feature is that a current corresponding to the collector current of the other transistor constituting the complementary push-pull circuit is detected by a current mirror circuit; The current and the collector current of one of the transistors that control the combrimentano push-pull circuit are passed through a common load resistor, and a full-wave rectified output of the input AC signal is obtained by the voltage across the load resistor, and Negative feedback is provided from the commonly connected emitters of the two transistors that control the complementary push-pull circuit to an amplifier connected at the front stage of the complementary push-pull circuit and to which an input AC signal is applied. It's what I did.

This invention will be explained below based on the embodiment shown in the drawings.

FIG. 1 shows the structure of the absolute value detection circuit of this invention. This circuit takes an input from an input terminal IN through an input resistor R and has an amplification factor of A.

is larger than 1, and the output of this operational amplifier is connected to an NPN transistor Q. via a coupling capacitor C and a resistor R1. (one transistor) and the PNP type transistor Q2 (the other transistor) are input to the point where the respective bases are connected in common, and each emitter is connected in common and the emitter resistance Re
The collector of the transistor Q1 is connected to the power supply +Vcc through the resistor Rc, and the collector of the transistor Q2 is connected to the power supply +Vcc through the resistor R2 and the diode D1.
a complementary push-pull circuit connected to the collector of the transistor Q1 and the transistor Q
An NPN transistor Q3 (constituting a current mirror circuit together with the diode D1 and resistor R2) whose emitter is connected to the collector of the second circuit and the power supply Vcc via the collector, base, and resistor R3, and the common transistor Q3 of both circuits. A resistor connected between the output terminal OUT derived from the connection point between the resistor Rc serving as the load and the collector of the transistor Q1, the connection point between the emitters of both transistors Q1 and Q2 and the resistor Re, and the human power terminal of the operational amplifier AMP. Rf
A negative feedback circuit NF is configured.

In this circuit, the transistor Q1 amplifies the positive half-cycle output signal of the operational amplifier AMP, the transistor Q2 amplifies the negative half-cycle output signal of the amplifier AMP, and the diode D1 amplifies the base-emitter voltage of the transistor Q3. It was inserted to compensate for the rise.

In this circuit, the input AC signal applied to the input terminal IN is amplified by the operational amplifier AMP, and the positive half-cycle input voltage is such that the base-emitter voltage VBE of the transistor Q1 is VBEI (approximately 0.0 for a silicon transistor) as shown in FIG. 6 V, about 0.2 for germanium transistor
V), the transistor Q1 turns on, and a current flows through the path of the collector-emitter resistor Re of the transistor Q1 and the ground, causing a voltage drop across the resistor Re, and this voltage is applied to the feedback resistor. It is applied to the input terminal of the operational amplifier AMP via Rf in the form of a voltage having a phase opposite to the input voltage.

Is the output of the operational amplifier AMP a negative half cycle? When the voltage changes, the transistor Q2 turns on, and a current flows through the path of ground, resistor Re, emitter/collector resistor R2 of transistor Q2, diode D1, power supply, and Vcc, causing a voltage drop across the resistor Re.

This voltage is applied to the operational amplifier A through the feedback resistor Rf.
A voltage having a phase opposite to the input voltage is applied to the input terminal of the MP.

Furthermore, as the transistor Q2 turns on, a voltage drop occurs across the resistor R2 and the diode D, and the transistor Q3 is forward biased and turned on. A current flows through the path of resistor R3 - power supply - Vcc, and an output voltage of a negative potential appears at the output terminal OUT, regardless of the polarity of the input voltage.

In this circuit, if there is no negative feedback circuit NF, the transistor Q. (or Q2)
The nonlinear part of the base-emitter voltage vs. collector current characteristic of , that is, the voltage at the rising point of the collector current VB 'E
The response to a small input voltage below the voltage equivalent to 1 (VBE2) is zero, and a dead zone exists between VBE and -VBE2.

However, by providing a negative feedback circuit NF, the base
Since the emitter voltage vs. collector current characteristic is shown by a broken line rather than a solid line in Figure 2, the base-emitter voltage ■BE
The dead band between 1 and -■BE is v8E'1 to 1VBE'2
Narrow and narrow.

The dead band due to the base-emitter voltage vBE is improved by the feedback amount of the negative feedback circuit NF.

FIG. 3 shows another embodiment of this invention, in which a circuit in which a plurality of diodes D2 and D3 are connected in parallel with reversed polarity is included in the negative feedback circuit NF of the absolute value detection circuit shown in FIG. By inserting this diode circuit in series, an absolute value detection circuit having logarithmic compression output characteristics can be constructed, which can be applied to a peak meter circuit, etc.

As described above, this invention uses a current mirror circuit to detect the current corresponding to the collector current of the other transistor that constitutes the combimentary push-pull circuit, and uses this detected current and the combimentary push-pull circuit to The collector current of one of the transistors is passed through a common load resistor, and the voltage across the load resistor is used to obtain a full-wave rectified output of the input AC signal, and the complementary push-pull circuit is constructed. Since negative feedback is provided from the commonly connected emitters of the two transistors to the amplifier connected to the front stage of this complementary push-pull circuit and to which the input AC signal is applied, the base of the transistor used as the amplifying element The dead band area due to the emitter voltage ■BE can be improved by the amount of negative feedback, and the dead band area becomes narrower.

In addition, since there is no time constant element in the circuit, an absolute value detection circuit with fast response and good frequency characteristics can be obtained, and the structure is relatively simple, suitable for IC implementation, and can be constructed at low cost. have an effect.

[Brief explanation of drawings]

The figures all show examples of this invention. Fig. 1 is a diagram of the structure of the absolute value detection circuit, Fig. 2 is a characteristic diagram for explaining the operation, and Fig. 3 is an absolute value detection circuit with logarithmic compression characteristics added. It is a block diagram of a detection circuit. IN. ．． ．． Manual terminal, OUT. ．． Output terminal, Ri,
Rc, Re, R1-R3...Resistance, C...Capacitor, D1-D3...Diode, Q1-Q3...
・Transistor, +Vcc, -Vcc...Power supply, N
F...negative feedback circuit, AMP... operational amplifier.

Claims (1)

[Scope of utility model registration request] An amplifier to which an AC input signal is applied, a combinatory push-pull circuit consisting of an NPN transistor and a PNP transistor with the output of this amplifier supplied to each base and connected in push-pull; A load resistor connected between the collector of one transistor constituting the circuit and the power supply, and a signal corresponding to the collector current of the other transistor constituting the complementary push-pull circuit to another current path. and a negative feedback circuit that negatively feeds back a signal obtained at the commonly connected emitters of both transistors constituting the combimentary push-pull circuit to the amplifier. The collector current of one transistor constituting the push-pull circuit and the current flowing through the other current path of the current mirror circuit are made to flow in common through the load resistor, and a full-wave rectified output of the input AC signal is output from the load resistor. An absolute value detection circuit characterized in that it extracts.