JPS61118050A - Data receiver - Google Patents

Abstract

PURPOSE:To bring data fed to an input terminal of a demodulation circuit to a prescribed level by providing an amplifier circuit whose amplification factor is variable to the pre-stage of a band pass filter and using an output of the band pass filter to control the amplification factor of the amplifier circuit. CONSTITUTION:The amplifier circuit 4 whose amplification factor is variable is provided to the input side of the band pass filter 1. Then the data subjected to carrier modulation is amplified by the circuit 4 and the result is fed to an amplifier circuit 2 via the filter 1. The output of the circuit 2 is fed to a demodulation circuit 3 and also to a control circuit 5, where the level is detected. The amplification factor of the circuit 4 is controlled immediately based on the result of detection to control the output level of the circuit 2 to a predetermined constant level.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a data receiving apparatus for receiving carrier modulated data.

Conventional Structures and Problems Generally, when transmitting control communication data in key telephone devices, intercom devices, etc., the data is often modulated with a predetermined carrier before being transmitted. Therefore, in this type of equipment, when receiving the above data, the band pass filter 1 extracts the modulated data from the signal applied to the input terminal IN, as shown in FIG. The amplification circuit 2 amplifies the data, and then the demodulation circuit 3 demodulates the original data. However, in this type of device, when the distance of the data transmission line or the number of terminals changes, the line loss changes significantly, and the data applied to the input terminal of the demodulation circuit 30 changes as shown in Fig. 2 (a). ) of (b).

(As shown by /, the original data may become larger or smaller, and the demodulation circuit 3 may not be able to accurately demodulate the original data.) Therefore, if the data applied to the input terminal of the demodulation circuit 3 becomes extremely larger than the threshold voltage as shown in (b) of FIG. 2(a), , the data demodulated for the corresponding time td2 becomes temporally long as shown in Figure 2(b) (middle), and as shown in Figure 2(a)(c), the When the voltage becomes smaller than the threshold voltage, the data is no longer demodulated as shown in (c) of FIG. 2(b), which is extremely inconvenient.

OBJECTS OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned conventional drawbacks, and to provide an excellent data receiving apparatus that has a simple configuration and can always perform accurate demodulation.

Structure of the Invention In order to achieve the above object, the present invention provides an amplifier circuit with a variable amplification degree on the input side of a band-pass filter, controls the amplification degree of this amplifier circuit according to the output of the band-pass filter, The structure is such that the data applied to the input terminal of the demodulation circuit connected after the bandpass filter is always at a substantially constant level.

DESCRIPTION OF THE EMBODIMENT FIG. 3 is a schematic diagram of an embodiment of the data receiving apparatus of the present invention. In the figure, the same reference numerals as in FIG. 1 indicate the same elements as in FIG. There is. 4 is an amplifier circuit that is connected to the input side of the bandpass filter 1 and is capable of varying the amplification degree; 5 is an amplifier circuit that detects the output level of the amplifier circuit 2;
This is a control circuit that controls the amplification degree of the amplifier circuit 4.

In the above embodiment, if carrier modulated data as shown in FIG. applied. The output of the amplifier circuit 2 is applied to the demodulation circuit 3 and at the same time to the control circuit 5, where its level is detected. Then, the amplification degree of the amplifier circuit 4 is immediately controlled based on the detection result, and the output level of the amplifier circuit 2 is controlled to be at a predetermined constant level. Therefore, the output of the amplifier circuit 2 becomes K as shown in FIG. 4(b), and the demodulating circuit 3 demodulates the above data accurately as shown in FIG. 4(c).

That is, according to the above embodiment, even if the data applied to the input terminal IN is extremely large or small as shown in (b) and (c) of FIG. 4(a), the amplifier circuit 4.
At the stage where K is applied to the demodulation circuit 3 by the action of the control circuit 5, as shown in (b) and (c) of FIG. In the same way as in (a) of Fig. 4, the demodulation circuit 3
It will be demodulated accurately.

Effects of the Invention As is clear from the above-mentioned embodiments, the present invention provides an amplification circuit whose amplification degree can be varied before a band-pass filter, controls the amplification degree of this amplification circuit by the output of the band-pass filter, and controls the amplification degree of the band-pass filter. The input terminal of the demodulation circuit connected after the pass filter is configured so that the applied data is always at a substantially constant level. Therefore, according to the present invention, the line for transmitting the data is Even if the level of the data changes greatly due to changes in length or number of terminals, the data can always be accurately demodulated and received regardless of these changes, which is extremely advantageous in practice.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a conventional data receiving device, FIG. 2 is an explanatory diagram of the operation of the same device, FIG. 3 is a schematic configuration diagram of an embodiment of the data receiving device of the present invention, and FIG. 4 is a diagram showing the same implementation. FIG. 3 is an explanatory diagram of an example operation. 1...Band pass filter, 2...Amplification circuit, 3.
・Demodulation circuit, 4... Amplification circuit with variable amplification degree, 5.
・Control circuit, IN...input terminal, OUT...output terminal. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] An amplifier circuit whose amplification degree can be varied is provided in the front stage of a band pass filter that passes carrier-modulated data, and the amplification degree of this amplifier circuit is controlled according to the output level of the band pass filter, and the stage after the band pass filter is A data receiving device configured such that data applied to the input terminal of a demodulation circuit connected to the demodulation circuit is always at a substantially constant level.