JPS5822090Y2 - Meter drive circuit with logarithmic characteristics - Google Patents

Description

[Detailed description of the invention] This invention relates to a meter drive circuit in which the meter reading of the meter circuit has logarithmic compression characteristics by connecting a series circuit of a silicon diode and a resistor in parallel to the meter circuit. be.

2. Description of the Related Art Conventionally, level meters have been used in various electronic devices, such as audio devices, to display input and output levels.

However, if the level of the input signal that drives the level meter is extremely linear, it is possible to display the meter reading proportionally; however, if the input signal increases and changes exponentially, Not only is this inconvenient due to the display range, but it also makes it difficult for the viewer to see.

Therefore, when increasing the input signal exponentially,
It is common practice to display a meter using the logarithmic value of the input signal, but a dedicated and expensive logarithmic amplifier is used for this display, and the configuration of the meter drive circuit is often complicated. The reality is that there are.

This invention is characterized by connecting a series circuit of a diode and a resistor in parallel to the meter circuit without using a dedicated and expensive logarithmic amplifier.With this simple connection configuration, the meter reading has logarithmic compression characteristics. The purpose is to provide a meter drive circuit that is inexpensive and has good temperature characteristics.

The present invention will be explained below with reference to FIGS. 1 and 2.

First, before going into a specific explanation of the present invention, the diode connected to the meter circuit will be explained.

This diode has forward characteristics as shown in FIG. 1, and the voltage at point A is about 0.6V, that is, it is not a germanium diode but a silicon diode.

1. The operating range of the silicon diode used in this invention is the rising part of the silicon diode, that is, approximately the voltage at point B, and the voltage at point C, where the differential coefficient is large, or at a voltage larger than that. Not used in regions.

Therefore, the use of silicon diodes in this invention is different from the use in protection from excessive input of meters or in clipper circuits, and does not utilize the saturation characteristics of forward voltage; This is completely different.

This is because if the saturation characteristics of silicon diodes were to be used, the meter reading would appear too compressed, making it rather difficult to read.

To explain this idea with reference to Fig. 2, a series circuit of a resistor R2 and a silicon diode D3 and a series circuit of a resistor R3 and a meter M are connected in parallel to a voltage doubler circuit consisting of germanium diodes D1 and D2 and capacitors C1 and C2. It is something that

When the input signal S to be indicated to the meter M is full-wave rectified by the voltage doubler circuit via the resistor R1, the smoothed DC voltage is supplied to the silicon diode D3 and the meter M via the capacitors C1 and C2. Ru.

Here, if the currents flowing through the silicon diode D3 and the meter M are respectively ■dtIM, the total current Is is ■5=
It is expressed as Id+IM.

The current Id is the current that flows when the value of the DC voltage is 0.6 V or more, but if the current ■ has anti-logarithmic characteristics, the current IM is IM = Is - Ib. should also be a logarithmic characteristic.

That is, if a silicon diode is connected in parallel to the meter M, the reading from the meter M will have logarithmic compression characteristics.

In this case, the degree of compression is adjusted by the resistor R2yR3, and the old resistor R1 is provided for adjusting the sensitivity of the meter M.

It should be noted that the experimental results of this invention using a meter M with a decibel (dB) scale show that almost accurate logarithmic compression characteristics were obtained in the range of +3 to -30 dB.

Of course, by adjusting the resistors R2 and R3, free compression characteristics can be obtained.

As explained above in detail, this invention is one in which a silicon diode is connected in parallel to the meter so that the meter reading has logarithmic compression characteristics.

Moreover, since its logarithmic compression characteristics are accurate over a considerable range, it will be obvious that it can be used in place of expensive logarithmic amplifiers.

Therefore, according to this invention, it is possible to provide an inexpensive meter drive circuit with fewer parts and fewer failures.

There are many possible uses for this invention, but one of the most suitable applications for this invention is, for example, a meter circuit for an audio power amplifier.

[Brief explanation of drawings]

FIG. 1 is a forward characteristic diagram of a silicon diode, and FIG. 2 is an embodiment of this invention using a silicon diode. R1pR2*R3...Resistance, D3...
Silicon diode, M...meter, S...
...Input signal indicated by meter.

Claims (1)

[Scope of utility model registration request] A series circuit of a resistor and a silicon diode is connected in parallel to a series circuit of a resistor and a meter, and when the DC voltage of the input signal indicated by the meter is applied to the two series circuits, the silicon diode rises in the forward direction. Using the anti-logarithm characteristic of the
A patented meter drive circuit characterized in that it is configured to have logarithmic compression characteristics due to the current flowing through a silicon diode.