JPS5892152A - Control circuit for automatic frequency characteristics - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] The present invention provides a signal (hereinafter referred to as a downlink signal) sent from the center in the rear body circuit of a terminal that receives character and graphic information.
This is a book about a circuit that automatically controls and flattens the slope of the W wavenumber characteristic of .

In the conventional operation circuit, a vibration cape circuit that can set a predetermined frequency characteristic with a manual changeover switch is added, but since the step is large, the slope of the m* number characteristic of the downlink signal is There is quite a bit left and %Also,
Connecting the telephone port 114 terminal to the center causes a change in the volume, which worsens the main function and causes problems! -Naru, koji g
The drawback is that it reduces the eye opening of SE and worsens the bit error rate.

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art by eliminating <15.
It is possible to provide a return circuit that automatically controls and flattens the slope of the frequency characteristic of the downlink signal.

The downlink signal after the automatic gain control of the present inventor is l! l wrinkle BPF (
Takahan Obi-Aya Filter), Low Furnace BPF (Low-furnace Obi-Aya Filter)
They are separated into their respective frequency components, each detected and rectified, and the difference is amplified by a differential amplifier circuit, and the output voltage is changed by a diode or other equivalent resistance. The horizontal e1. This is a book that is characterized by

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained with reference to the drawings. ! FIG. 1 shows an embodiment of the automatic frequency characteristic control circuit of the present invention, FIG. 2 shows the wave number characteristics of the amplifier circuit 30II, and FIG. 3 shows the control operation of the automatic 1ili1 wave number characteristic control circuit under various conditions.

@Figure 1 shows that the downlink signal sent from the center using the telephone line is a hybrid transformer, and the downlink signal H
The signal is transmitted to the automatic frequency characteristic control circuit 1 according to the present invention through a PF (high-pass filter) and an amplitude modifier, and is then transmitted to the automatic gain control circuit 2 at the next stage.

A part of the output signal of the automatic gain control circuit 2 is a high-frequency BPF 4.
(For example, about 2200±400Hg) and (l[
' It is transmitted to BPF6 (for example, about 1000±400Hg). The signal passing through the high jdBPF4 is detected and
It is converted into direct current by the rectifier circuit 5, and is connected to the O terminal of the differential amplifier circuit 8. The signal that has passed through l6 is converted into direct current by the detection rectifier circuit F and is supplied to the O terminal of the n1 differential amplifier circuit 8. This differential amplifier circuit 8 amplifies the voltage difference between the terminals 1 and 1, and supplies the amplified voltage to the anode of a diode 9a in the control circuit 9. Assuming that the equivalent resistance of this diode 9a is R, this R decreases as the output voltage of the differential amplifier circuit 8 increases (approaches 0Ω), and conversely increases as the output voltage decreases (approaches ooΩ). By providing the amplification characteristic 3 with WpUtIt number characteristics such as characteristics 10, 11, and 12 in FIG. 2, automatic &i1 wave number characteristic control becomes possible. Characteristics in Figure 2 '10, 11.1
2 shows the case where the equivalent resistance of the diode 9a is R, oo, O. Normally, by setting R# R1 to 111, the 119 characteristic of the amplifier circuit 3 becomes flat.

Now, if for some reason the downstream signal output of the automatic gain control circuit 2 becomes a low level at the low frequency 1i1ff number and a high level at the high frequency as shown in FIG. 3(a), then the high frequency BPF4. ■ of the differential amplifier circuit 8 through the detection circuit 5
Terminal voltage and low range BPF6. The voltage difference between the terminals of the differential amplifier circuit 8 after passing through the detection rectifier circuit becomes larger than normal, so the output voltage of the differential amplifier circuit 8 becomes larger than when the current is energized, and R approaches OΩ. %l/ES diagram (
As shown in 1)), the frequency characteristics of the amplifier circuit 30 are low gain in the high range and high gain in the low range, so the frequency characteristics of the output of the amplifier circuit 3 and the output of the automatic gain control circuit 2 are as shown in Fig. 3(e). The result is tY flat. Figure 3(d) (151(f)
When the downstream signal output of the automatic gain control circuit 2 is flat at l, the downstream signal output of the automatic gain control circuit 2 is in the low range j1! for some reason. It shows the control operation when the wave number becomes high level and the Takatsuka frequency becomes low level.

In this way, it is possible to perform automatic frequency characteristic control that automatically flags whether the frequency characteristic of the downlink signal is inclined to the high or low side.

The present invention eliminates fluctuations in frequency characteristics caused by the type of transmission cable used as a telephone line or the amplitude imbalance of the demodulation circuit in the terminal, so the eye opening during decoding becomes larger and the bit error rate increases. is improved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the automatic frequency characteristic control circuit according to the present invention, and FIG.
! 1tIJt number characteristic diagram. FIG. 3 is a frequency distribution diagram showing the control operation of the automatic frequency characteristic control circuit under various conditions. 1...Auto frequency #! i-characteristic control circuit number 00. High BPF 5...Low BPF 9...Control circuit agent Patent attorney Fumi Watanabe Yusai try l −−−−−−−−−−1−−−−−−−−−−−− ---
−−−−−−J Fang 2 Figure

Claims (1)

[Claims] The back of the terminal that receives text and graphic information using the telephone line.
The circuit includes a high band filter that extracts high frequency components of the signal transmitted from the center, a low band filter that extracts low frequency components, and 2 that detects and rectifies the outputs of the two band filters, respectively. A # wave PWF circuit, a differential amplifier circuit that amplifies the difference between v12 detection and rectification outputs, a control circuit that changes the equivalent resistance depending on the output voltage of the 1 differential amplifier circuit, and transmission from the center by the control circuit. An automatic 8-wavenumber characteristic control circuit characterized in that it is expanded by a W increase circuit that controls the frequency characteristics of a signal.