JPS642036B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rectification time constant circuit, and when integrating a rectification time constant circuit using silicon diodes, the present invention approximates excellent characteristics obtained with a rectification time constant circuit using germanium diodes. The purpose of the present invention is to provide a rectifier time constant circuit that can obtain the following characteristics.

Conventionally, in gain control devices such as noise reduction devices in audio systems and audio limiters that control the audio signal level, a rectification time constant circuit is used to convert the control signal of the audio signal. Germanium diodes and silicon diodes are used as rectifying elements. Germanium diodes and silicon diodes basically have different forward current vs. forward voltage characteristics (hereinafter referred to as I _F - V _F characteristics) and reverse current vs. reverse voltage characteristics, so germanium diodes were used. A rectification time constant circuit and a rectification time constant circuit using silicon diodes are different in input signal level versus control signal level characteristics and circuit output impedance characteristics. for example,
Comparing the I _F -V _F characteristic curve of a germanium diode and the I _F -V _F characteristic curve of a silicon diode shown in Fig. 1, at the same forward voltage,
The forward current in a germanium diode is much larger than that in a silicon diode. That is, the impedance characteristics of a silicon diode rectifier circuit are compared to those of a germanium diode rectifier circuit, and for example, when the forward voltage applied to the diode is 0.2V,
500-1000 times higher.

Such input signal level versus control signal level characteristics are related to signal level compression characteristics and signal level expansion characteristics in a noise reduction device, and are related to signal level compression characteristics in an audio limiter. The output impedance characteristic of the circuit is also related to the control time constant, or attack time, in each device.

Therefore, in a germanium diode rectifier time constant circuit, the internal resistance of the diode at the actual operating level is 1/500 to 1/1000 lower than that of a silicon diode, so the control time constant can be set using an external fixed resistor. Since it can be easily set using a capacitor, it is often used in the rectification time constant circuit of noise reduction equipment. However, germanium diodes are not suitable for monolithic integrated circuits, so silicon diode rectifier time constant circuits are used for rectifier time constant circuits designed for integrated circuits.

FIG. 2 shows a circuit diagram of an example of a conventional rectification time constant circuit. In FIG. 2, an input signal entering terminal 1 is supplied via capacitor C ₁ and resistor R ₁ to amplifier 2 which outputs an in-phase output signal. The output signal from the amplifier 2 is supplied to the diode _D1 , and at the same time, the output signal is branched to the amplifier 3, which outputs a negative phase output signal.
is supplied to The output signal from amplifier 3 is fed to diode _D2 . The cathode sides of diode _D1 and diode _D2 are connected to resistor _R4 and resistor _R5 , and the rectified outputs from diode _D1 and diode _D2 appear across resistor _R4 . Further, this rectified output is supplied to a time constant circuit consisting of a resistor _R5 and a capacitor _C2 , and is outputted from a terminal 4 as a control voltage. FIG. 5 is a characteristic diagram showing the relationship between the input signal level and the control voltage when germanium diodes or silicon diodes are used as the diodes D ₁ and D ₂ in the above circuit. In Fig. 5, curve a is the input signal level versus control voltage curve for a germanium diode, and curve b is for a silicon diode. Characteristics are very different. In FIG. 5, the gain of the amplifier 2 is changed so that the control voltage levels of the silicon diode rectifier circuit and the germanium diode rectifier circuit are equal at the large signal level.

In this way, the silicon diode rectifier time constant circuit has a high internal resistance of the diode, and since the internal resistance is inversely proportional to the input signal level, at the actual operating level, the attack time is long at small signal levels, and the attack time is long at large signal levels. The attack time changes significantly depending on the input signal level, sometimes becoming shorter. Therefore, in conventional silicon diode rectification time constant circuits, the internal resistance of the silicon diode is directly related to the control time constant, so there are drawbacks such as the control time constant not being fixed due to variations in the internal resistance of the silicon diode. Ta. Furthermore, since there is a direct relationship between the control time constant and the noise modulation phenomenon that occurs as a side effect in the noise reduction device, a change in the control time constant has the disadvantage of adversely affecting the noise modulation phenomenon.

The present invention eliminates the above-mentioned drawbacks, and one embodiment thereof will be described in conjunction with FIGS. 3 to 5.

FIG. 3 shows a circuit diagram of an embodiment of the rectifying time constant circuit of the present invention. In FIG. 3, the input signal e _i that enters the terminal 5 is passed through the first half-wave rectifier circuit 6 which is composed of resistors R ₁₁ , R ₁₂ , R ₁₃ , silicon diodes D ₁₁ , D ₁₂ and amplifier I _c11. and is supplied to an inverting amplifier 7 with a gain of 1. Output signal e ₁ of inverting amplifier 7
are resistors R ₁₄ , R ₁₅ , R ₁₆ , silicon diodes
The signal is supplied to a second half-wave rectifier circuit 8 composed of D ₁₃ , D ₁₄ and an amplifier I _c12 . Therefore, a positive half-wave rectified output signal corresponding to the negative half cycle of the input signal e _i is generated across the resistor R ₁₃ of the half-wave rectifier circuit 6, and the resistor R ₁₆ of the half-wave rectifier circuit 8 A positive half-wave rectified signal corresponding to the negative half cycle of the signal _{e1, which is the inversion of the input signal ei ,} is generated at both ends of the signal e1. The half-wave rectified signal on both ends of resistor _R13 and the half-wave rectified signal on both ends of resistor _R16 are added to obtain a double-wave rectified signal _e2 , and this double-wave rectified signal _e2 is obtained from resistor _R17 and capacitor _C3 . It is converted into a control voltage E ₀ through an integrating circuit, and outputted from the output terminal 7. The half-wave rectifier circuit 3 and the half-wave rectifier circuit 4 have the same circuit configuration, circuit constants, operation, characteristics, etc. Note that the resistor R ₁₂ constitutes a first negative feedback circuit, and the resistor R ₁₃ constitutes a second negative feedback circuit. Similarly, the above resistance
R ₁₅ constitutes a third negative feedback circuit, and the resistor R ₁₆
constitutes a fourth negative feedback circuit. The diode D ₁₁ used in the half-wave rectifier circuit 6 and the diode D ₁₃ used in the half-wave rectifier circuit 8 have a smaller negative feedback amount during the positive half cycle of the input signal in each circuit. It is used to prevent the circuit from becoming saturated and half-wave rectification not being performed correctly.

FIG. 4 shows an equivalent circuit of the half-wave rectifier circuit ₆ in FIG.
The forward internal resistance of D ₁₂ is designated R _df . Fourth
In the equivalent circuit shown in the figure, the output signal e _p is output from the terminal 10 in response to the input signal e _i that enters the terminal 5.
The ratio of the circuit gain e _p /e _i is expressed by the following equation.

e ₀ /e _i = -R ₁₂ /R ₁₁・R ₁₃ /R ₁₂ +R _df +R ₁₃ ...(1) Furthermore, the output impedance of this equivalent circuit Z _p
is expressed by the following equation.

Z _p = R _df − R ₁₃ / R ₁₂ + R _df + R ₁₃ ...(2) This output impedance Z _p is due to the negative feedback effect of the diode's forward internal resistance R _{df .}
This resistance is equivalent to changing to
R _df ′ can be expressed as follows.

R _df ′=R _df・R ₁₃ /R ₁₂ +R _df ′+R ₁₃ ...(3) Therefore, equations (2) and (3) can be used during the negative half cycle of the input signal e _i , but when the positive During the half cycle of , the internal resistance R _df of the diode D ₁₂ becomes infinite, so the output impedance Z′ _p in this case becomes as follows.

Z′ _p = R ₁₃ Thus, in this example, the diode D ₁₂
is connected to the feedback loop, the internal resistance of diode _D12 can be reduced by the amount of feedback, and the influence of this internal resistance on the control time constant of the rectifier time constant circuit can be reduced.

FIG. 5 is a characteristic diagram showing the relationship between the input signal level and the control voltage level when the output impedance Z _p is changed. As mentioned above, curve a in the figure is a characteristic curve of a rectifying time constant circuit using germanium diodes, and curve b is a characteristic curve of a conventional rectifying time constant circuit using silicon diodes. Curves c, d, e, and f in the figure show characteristic curves when the resistance R ₁₂ is varied in the rectifying time constant circuit of the present invention. R ₁₁ = R ₁₂ and
If R ₁₂ << R ₁₃ , this circuit approaches the characteristics of curve b; if R ₁₁ < R ₁₂ and R ₁₃ < R ₁₂ , this circuit approaches the characteristics of curves c, d, e, a; _R13
At <<R ₁₂ , the characteristics can be approximated to those of the curve f.

In this way, in the present invention, arbitrary characteristics can be obtained using the resistor _R12 , and even a rectification time constant circuit using silicon diodes can achieve input signal level vs. control equivalent to a rectification time constant circuit using germanium diodes. The voltage level relationship can be obtained.

Next, the control time constant in the rectification time constant circuit of the present invention will be explained. The attack time T _a is expressed by the following formula.

T _a = (R _df ′+R ₁₇ ) C ₃ (5) Moreover, the recovery time T _r is expressed by the following formula.

T _r = (R ₁₃ · R ₁₆ / R ₁₃ + R ₁₆ + R ₁₇ ) C ₃ ...(6) Therefore, the recovery time T _r is set only by fixed resistors R ₁₃ , R ₁₆ , R ₁₇ and capacitor C ₃ Therefore, there is no need to distinguish between germanium diodes and silicon diodes, but the attack time T _a depends on the resistance including the internal resistance of the diode.
Since it is directly related to R _df ', it is necessary to find the value of resistance R _df ' that matches the internal resistance of the germanium diode. However, in general, when setting the circuit constants in the germanium diode rectifier time constant circuit shown in Figure 2,
_{The resistance R 5 is}
R _df1 =R _df2 , and R _df1 <R ₅ . Therefore, in reality, the attack time is almost determined by R ₅ ×C ₂ . This can be similarly applied to the rectifier time constant circuit of the present invention; if the resistance R _df ' is set such that R _df '< R ₁₇ , the attack time T _a is almost determined by R ₁₇ × C ₃ . . Therefore, if the R _df ' and R _df1 characteristics with respect to the input signal level are similar, it is possible to realize a silicon diode rectifier time constant circuit that is almost compatible with the conventional germanium diode rectifier time constant circuit in terms of attack time T _a . It is.

As described above, the rectification time constant circuit according to the present invention includes a first amplifier to which an input signal is supplied, a first negative feedback circuit extending from the output side of the first amplifier to the input side, and a first negative feedback circuit of the first amplifier. a first half-wave rectifier circuit comprising a first silicon diode connected to the output side and a second negative feedback circuit extending from the output side of the first silicon diode to the input side of the first amplifier; a second amplifier to which an input signal is supplied via an inverting amplifier with a gain of 1; a third negative feedback circuit connected from the output side of the second amplifier to the input side; and a third negative feedback circuit connected to the output side of the second amplifier. a second silicon diode, and a second silicon diode from the output side of the second silicon diode.
A second half-wave rectifier circuit consisting of a fourth negative feedback circuit leading to the input side of the amplifier and each output of the first and second silicon diodes are combined to obtain a double-wave rectified signal, which is integrated. Since the circuit is configured with an integrating circuit that outputs a control voltage using silicon diodes, it is easy to integrate the circuit using silicon diodes, and it is possible to obtain almost the same input signal level vs. control voltage level characteristics as a conventional germanium diode rectifier time constant circuit. This makes it possible to have the excellent features of a germanium diode rectifier time constant circuit against noise modulation, and the rectifier time constant circuit has almost no effect on the control time constant even if there is some variation in the internal resistance of the diode. It has features such as being able to design

[Brief explanation of drawings]

Fig. 1 is a characteristic diagram showing the relationship between forward current and forward voltage of a diode, Fig. 2 is a circuit diagram showing an example of a conventional rectification time constant circuit, and Fig. 3 is a circuit diagram showing an example of the rectification time constant circuit of the present invention. FIG. 4 is an equivalent circuit diagram of the half-wave rectifier circuit of FIG. 3, and FIG. 5 is a characteristic diagram showing the relationship between input signal level and control voltage level. 2...Amplifier, 3...Inverting amplifier, 6, 8...
Half-wave rectifier circuit, 7...Inverting circuit, R1 _{to R17} ...Resistor, _C1 to _C3 ...Capacitor, _D1 , _D2 , _D11 to _D14
……diode.

Claims (1)

[Claims] 1. A first amplifier to which an input signal is supplied, a first negative feedback circuit extending from the output side of the first amplifier to the input side, and connected to the output side of the first amplifier. a first half-wave rectifier circuit comprising a first silicon diode and a second negative feedback circuit extending from the output side of the first silicon diode to the input side of the first amplifier; is supplied via an inverting amplifier with a gain of 1; a third negative feedback circuit extending from the output side of the second amplifier to the input side;
a second half-wave consisting of a second silicon diode connected to the output side of the amplifier; and a fourth negative feedback circuit extending from the output side of the second silicon diode to the input side of the second amplifier. A rectifier comprising: a rectifier circuit; and an integrating circuit that combines the outputs of the first and second silicon diodes to obtain a double-wave rectified signal, integrates the signal, and outputs a control voltage. constant circuit.