JPS6317379B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field: The present invention relates to a timing signal extraction method for a modem, a modem, connected to a line, and more particularly to a timing signal extraction method for creating a timing signal from a received signal.

<Technical Background> Generally, a modem demodulates a received signal received from a line, reproduces received data based on the obtained baseband signal, and supplies it to a receiving terminal as received data.

Furthermore, in order to synchronize with the transmitting terminal, such devices extract a timing signal component from the received baseband signal to create a timing signal, and supply this to the receiving terminal.

<Prior Art> FIG. 1 is a block diagram of a conventional timing extraction method.

In the figure, 1 is a demodulation unit that removes the carrier signal from the received signal and demodulates the baseband signal i of the imaginary component into the baseband signal of the real component, and 2r and i are the units corresponding to each component. It is a filter that controls the frequency of the timing signal to be extracted.
If it is set to 0, then something that waves at a frequency of 0/2, 3
4 is an adder; 5 is an arithmetic unit that calculates the square of the absolute value of each extracted component;
is a filter that extracts the timing signal.

Explain the operation.

The received signal is demodulated by a demodulator 1, and a timing signal component 0/2 signal related to the timing signal is extracted from the demodulated baseband signal by filters 2r and 2i.

The extracted frequency 0/2 signal is sent to the calculation unit 3.
r, 3i and the adder 4, and the error between the carrier signal for demodulation used in the demodulator 1 and the carrier signal of the actual received signal is removed, and is expressed by the following equation including the frequency component of the timing signal. A signal is output.

y=((t)) ² =A ² cos ² 0/2t...(1) In the same equation, t is time, A is amplitude, and (t) is the timing signal extracted by filters 2r and 2i. . The signal y shown in the equation has a relationship with the timing frequency as shown in the following equation.

y=A ² /2(1+cos0t)...(2) Therefore, the filter 5 with a wave band at frequency 0
Therefore, the timing signal (cos0t) can be extracted by waveforming this signal y.

However, such a conventional timing signal extraction method includes a DC component of A ² /2 as shown in equation (2) above. That is, at the time when a carrier signal is received, this DC component becomes a step function, so it has the disadvantage that it takes time (draw-in time) until a so-called step response signal is output and a timing signal is extracted.

<Objective of the Invention> An object of the present invention is to provide a timing extraction method which eliminates the above-mentioned drawbacks, eliminates this step response, and allows a timing signal to be retrieved at high speed.

<Summary of the Invention> In order to achieve the above object, the present invention takes into consideration that the step response occurs because the timing signal is extracted from the signal calculated as a result of the above calculation, and calculate the components,
This DC signal component is removed before being supplied to the final stage filter from which the timing signal is taken out, and an embodiment will be described in detail below.

<Embodiment> FIG. 2 is a block diagram of an embodiment of the present invention. In the figure, the same parts as those used in FIG. 1 are designated by the same numbers. In addition, 6 is a DC component calculation circuit;
7 is a low-pass filter, and 8 is a DC component subtraction section.

The operating principle will be explained.

Similar to what was explained with reference to FIG. 1 above, the adder 4 outputs the signal y of equation (2) above.
Here, times t ₂ (t ₂ = t ₁ + π/2), t ₃ (t ₃ = t ₁ + π), t _{4 are} sequentially added by π/2 to a predetermined time t 1.
The values y ₂ , y ₃ , and y ₄ of the signal y at (t ₄ =t ₁ +3/2π) are calculated as follows.

t=t ₁ y ₁ =A ² /2 (1+cos0t ₁ ) ...(3) t=t ₂ y ₂ =A ² /2 (1-sin0t ₁ ) ...(4) t=t ₃ y ₃ =A ² / 2(1−cos0t ₁ ) …(5) t=t ₄ y ₄ =A ² /2(1+sin0t ₁ ) …(6) Therefore, add the signals y ₁ and y ₃ , y ₂ and y ₄ that are separated by π By multiplying the value by 1/2, the DC signal component "A2/2" can be created.

That is, in FIG. 2, first the signal y is sent to the delay section 6.
A signal delayed by 1,62 and advanced by a time π is created. Next, the value "1/2" stored in the register 63' is multiplied by the multiplier 63, and the result is set as one input of the adder 65. On the other hand, the multiplier 64 multiplies the signal delayed by π with the value "1/2" stored in the register 64'. A DC component is created by adding the obtained signal and the signal delayed by the delay sections 61 and 62 and obtained by calculation. The created DC component signal is supplied to a DC component subtraction unit 8 via a low-pass filter 7. The DC component subtraction unit 8 subtracts the DC component obtained as described above from the signal y, and supplies the filter 5 with a timing signal that does not include the DC component.

<Effects> As described above, according to the present invention, since the DC component is subtracted from the temporary timing signal extracted from the received baseband signal before passing it through the timing signal extraction filter, there is no step response. ,
This has the effect that the retraction time is also shortened.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional timing signal extraction method, and FIG. 2 is a block diagram of an embodiment of the present invention. In the figure, 1 is a demodulator, 2r and 2i are filters, and 3
3i is an arithmetic unit, 4 is an addition unit, 5 is a timing signal extraction filter, 6 is a DC component creation unit, 7 is a low-pass filter, and 8 is a DC component subtraction unit.

Claims (1)

[Claims] 1 A wave generator that extracts a timing signal component included in a received baseband signal, a synthesizer that synthesizes the timing signal components extracted from the wave generator, and a wave generator that generates the frequency of the timing signal from the synthesized signal. In a timing signal extraction method for creating a timing signal, a DC component is calculated from the timing signal created by the synthesis, and the DC component is subtracted from the timing signal created by the synthesis to obtain the timing signal. A timing signal extraction method featuring: