JPS5834056B2 - automatic equalizer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit configuration of an automatic equalizer, and particularly to an automatic equalizer that automatically adjusts the tap gain of a transversal filter suitable for transmitting analog signals.

Conventionally, in an automatic equalizer using a transversal type variable filter, the tap gain was adjusted by sending out a pulse waveform at fixed time intervals from the transmitting side, and by adjusting the code amount interference of the received pulses on the receiving side. A common method is to adjust each tap gain so as to minimize it.

In this method, when the signal waveform itself is a synchronous signal waveform, such as in data transmission, the degree of equalization is directly linked to the signal transmission characteristics, and a part of the transmitter/receiver can be used as an automatic equalizer circuit. C
It has advantages.

However, if the signal to be transmitted is an asynchronous signal such as an uncoded audio signal or image signal, it is necessary to provide a pulse generator or timing analysis circuit just for equalization adjustment and perform synchronization adjustment. However, in order to eliminate the above-mentioned drawbacks of the conventional example, the present invention transmits white noise from the transmitting side and transmits white noise from the receiving side. It is characterized by determining the autocorrelation of the received noise waveform and determining each tap gain based on the value of this autocorrelation function, and its purpose is to provide a simple automatic equalizer suitable for transmitting asynchronous signals. be.

Hereinafter, embodiments will be described in detail with reference to the drawings.

The figure shows an embodiment of the present invention, in which 1 is a transmitter;
2 is a transmission line, 3 is a signal input terminal, 4 to 7 are delay lines each having a delay time of T seconds, 8 to 11 are control circuits that control the tap gain of each delay line, and 12 is a main signal and four taps. A signal synthesis circuit, 13 to 16 are delay lines each having a delay time of T seconds, 17 to 20 are multipliers for the output signal of the synthesis circuit 12 and the tap signals of delay lines 13 to 16, and 21 to 24 are integrators. It is a vessel.

Next, the operation of this embodiment will be explained.

First, when the transmitter 1 transmits white noise with a flat frequency spectrum, a noise signal subjected to transmission distortion via the transmission line 2 reaches the input signal terminal 3.

Let the waveform of this input signal be n i (t), and the tap gains of tap gain control circuits 8 to 11 be Qt and q2, respectively.
．． If qL+q4, then the output signal n of the synthesis circuit 12.

(1) becomes as follows.

This output signal n,(t) is outputted to T by delay lines 13-16.

The signal is delayed by 2T, 3T, and 4T, and the delayed signal and the undelayed signal are multiplied together and then integrated.

Each integral output is connected to a control signal terminal of tap gain control circuits 8-11.

Also, each integral output bias, ψ (2'r) tψ (3T), ψ
(4T) is the output signal n of the combining circuit 12.

This is the autocorrelation function of (1) and can be expressed as follows.

However, since the autocorrelation function of any signal is the inverse Fourier transform of the power spectrum of the original signal, the output signal n.

If we express the power spectrum in (1) by α power and consider that the autocorrelation function is an even function, ψ(T),...
...The following relationship occurs between ψ(4T) and G(f).

That is, it can be seen that this ψ(T) is a coefficient when G(T) is expanded into a Fourier series with T as the fundamental period.

If we ignore the DC component of this G, we get the following relationship.

From now on, by changing the tap gains of the tap gain control circuits 8 to 11, the power spectrum TT
It is possible to change the magnitude of the cosine-like fluctuation characteristic with period T2v3 as T-1 and ■ with respect to TmuG(f), respectively.

For example, when the level of the prong signal of the tap gain control circuit 8 is changed, only the output level of the integrator 21 among the integrators 21 to 24 changes, so the tap gain control circuit 8 - synthesis circuit 12 - delay line 13 output By setting the gain and direction of the closed loop circuit composed of the signal line 17 and the integrator 21 to appropriate values, it is possible to reduce cosine-shaped transmission distortion with one period of 1/T hertz.

Furthermore, tap gain control circuits other than tap gain control circuit 8 can be expected to have similar effects on cosine transmission distortion with periods of 1/2T, 1/3T, and 1/4T. It becomes possible to perform equalization by approximating a transmission band with a width of 1/T Hertz by a cosine series up to the fourth order.

As explained above, according to the present invention, a white noise generator is provided on the transmitting side, a device mainly consisting of a correlator and a tapped delay line is provided on the receiving side, and each By adjusting the tap gain, a simple automatic vase suitable for analog signals can be configured.

[Brief explanation of the drawing]

The figure is a block diagram of one embodiment of the present invention. 1...Transmitter, 2...Transmission line, 3...
...Signal input terminal, 4-7...Delay line with delay time T seconds, 8-11...Tap gain control circuit, 12...Main signal and Synthesizing circuit for four tap signals, 13-16...delay line with delay time of T seconds, 17-20...multiplier, 21-24...
...integrator.

Claims (1)

[Claims] 1 One of two terminal devices connected to each other via a transmission line is provided with a white noise generator, the other is a transversal type filter consisting of a tapped delay line and a circuit for synthesizing each tap output, and each A control circuit that controls tap gain,
and a correlator for calculating the autocorrelation function of the input signal,
Send white noise from one terminal device to the transmission path, find the autocorrelation function of the noise waveform received at the other terminal device, and calculate each tap gain of the tapped delay line as the delay time of the corresponding tap of the same noise waveform. An automatic equalizer characterized by automatically adjusting according to a value of an autocorrelation function corresponding to .