JPH0638586B2 - √ f Automatic gain control equalizer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] In the gradient gain circuit, the capacitor that gives the gradient to be switched by the switch is given a potential even when it is not used, so that the impedance change does not occur in the capacitor when switched and the noise is eliminated. It was done like this.

[Industrial application field]

The present invention compensates for the loss of a subscriber line between a digital transmission type exchange and a terminal device. Regarding the improvement of.

Regarding the loss characteristics of the subscriber line, if the wire diameter is the same, the flat loss and the slope loss change depending on the distance as shown in FIG.

Further, even if the distance is fixed, it changes due to temperature change and the like.

To compensate for this loss Is used.

this Has a flat gain circuit 4, a slope gain circuit 5, a roll-off circuit 6 and an automatic gain control circuit 7, as shown in FIG.
If the transmission rate is, for example, 200 Kbps, the output level at the point where the Nyquist frequency is 100 Kbps is monitored by the automatic gain control circuit 7, and the flat gain circuit 4 is controlled according to this level to compensate for the flat loss and The gain circuit 5 is controlled to compensate the tilt loss, and the roll-off circuit 6 rolls off. this Then, it is desirable that noise is not generated when the capacitor that gives the slope is switched in order to control the slope gain circuit 5 to compensate the slope loss.

[Problems to be solved by conventional technology and invention]

 FIG. 4 is a circuit diagram of a conventional gradient gain circuit.

In the figure, 1 is an operational amplifier, SW1 and SW2 are switches, and C
Reference numerals 1 and C2 are capacitors for giving a gradient, R1 and R2 are resistors, and Vref is a reference voltage.

FIG. 4 shows an example of the case where there are two capacitors that give inclination.

In the gradient gain circuit, the switches SW1 and SW2 are turned on / off in accordance with a control signal from the automatic gain control circuit 7 in FIG. 2 to switch the capacitors C1 and C2 that give a gradient on the input side of the operational amplifier 1 to adjust the gradient gain. The capacitor C2 is used in FIG.
1 is an example not used.

When the switch SW1 is turned on and the switch SW2 is turned off so that the capacitor C1 is used to change the tilt gain,
The voltage between the reference voltage Vref and the point A is applied to the capacitor C1, and the capacitor C1 is charged.

During this charging, the impedance of the capacitor C1 changes abruptly, which causes a problem that noise is generated from the output.

[Means for solving problems]

The above-mentioned problem is solved by the present invention, in which the potential of the gradient gain circuit is given to the capacitor that gives the gradient to be switched by the switch even when it is not used. Will be solved by.

[Action]

According to the present invention, since a potential is applied to a capacitor that gives a gradient even when it is not used, even if it is switched to use, the capacitor is not charged and the impedance does not change, so that noise is not generated. Disappear.

〔Example〕

FIG. 1 is a circuit diagram of a gradient gain circuit according to an embodiment of the present invention.

In the figure, 2 and 3 are knot circuits, SW3 and SW4 are switches,
V indicates the voltage of the same potential as the point A, and the same reference numerals indicate the same functions throughout the drawings.

The difference between FIG. 1 and FIG. 4 is that the switches SW3,
SW4 is provided. For example, when the switch SW2 is turned on by a control signal, the switch SW4 is turned off by way of the knot circuit 3, and when the switch SW1 is turned off, the switch SW3 is turned on by way of the knot circuit 2. This is the point I chose to do.

By doing so, for example, since the voltage having the potential difference between the reference voltage Vref and the point A is applied to the capacitor C1 which is not used in FIG. 1 through the switch SW3, the switch SW1 is turned on and the capacitor C1 is turned on. Even if C1 is used, it is not charged, so that impedance change does not occur and noise is not generated.

〔The invention's effect〕

As described in detail above, according to the present invention, there is an effect that noise can be eliminated even when the capacitor that gives the inclination of the inclination gain circuit is switched.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a gradient gain circuit according to an embodiment of the present invention, and FIG. 2 is FIG. 3 is a loss characteristic diagram of a subscriber line, and FIG. 4 is a circuit diagram of a conventional gradient gain circuit. In the figure, 1 is an operational amplifier, 2 and 3 are knot circuits, 4 is a flat gain circuit, 5 is a slope gain circuit, 6 is a roll-off circuit, 7 is an automatic gain control circuit, SW1 to SW4 are switches, and C1 and C2 are Capacitors, R1 and R2 are resistors, and Vref is a reference voltage.

Claims (1)

[Claims] 1. Of the gradient gain circuit, the electric potential is applied to the capacitor that provides the gradient to be used by switching even when it is not used.