JP2940920B2 - Costas loop demodulator - Google Patents

Description

Detailed Description of the Invention [Table of Contents] Outline Industrial application field Conventional technology [FIGS. 4, 5 and 6 (a) to (c)] Problems to be Solved by the Invention Means (Fig. 1) Operation (Fig. 1) Embodiment (Figs. 2-3) Effect of the Invention [Overview] Costas loop type that generates carrier wave (carrier) or clock recovery based on baseband data For demodulators, the purpose is to make the range for frequency pull-in variable, to facilitate frequency pull-in even at low transmission rates, and to enable stable demodulation. A frequency pull-in assisting section for giving a required range for frequency pull-in to the output voltage-controlled oscillator control signal, based on the control signal from the sweep / track control signal generating section, The frequency pull-in range to be added to the voltage-controlled oscillator control signal set by the frequency pull-in auxiliary unit is set to be large when the voltage-controlled oscillator is in the sweep mode, and is set to be small when the voltage-controlled oscillator is in the track mode. And a protection circuit for prohibiting the frequency pull-in assisting unit from changing the frequency pull-in range for a predetermined time after the sweep mode is switched to the track mode.

[Industrial applications]

The present invention relates to a Costas loop type demodulator that generates carrier wave (carrier) recovery or clock recovery based on baseband data.

In the case of synchronous detection, a circuit for reproducing a carrier having the same phase as the carrier component of the modulated input wave is required on the receiving side. As such a carrier recovery circuit on the demodulation side, for example, there is a Costas loop.

[Conventional technology]

Fig. 4 shows a four-phase system using a conventional Costas loop demodulator.
FIG. 4 is a block diagram of a PSK demodulator. In the four-phase PSK demodulator shown in FIG. 4, for example, a QPSK wave in a 70 MHz band is frequency-converted by a frequency conversion circuit 21 in accordance with a signal from a synthesizer 20, After being filtered by the bandpass filter 22 and the gain adjusted by the variable attenuator 23,
In the 90 ° hybrid 1, the signals are divided into two signals having different phases by 90 °.

Each signal is input to a carrier reproduction circuit CRC via mixers 2A; 2B, low-pass filters 3A; 3B for band limitation, and A / D converters 10A; 10B.

The carrier recovery circuit CRC has functions of phase detection and a loop filter. The output of the loop filter portion is input to the voltage controlled oscillator (VCO) 6 via the D / A converter 11, and the voltage of the voltage controlled oscillator 6 Output is each mixer 2A, 2B
To be entered.

24 is a bit timing recovery (clock recovery circuit), and the output from this clock recovery circuit 24 is A / D
Input to converters 10A and 10B.

As shown in FIG. 5, the carrier recovery circuit CRC includes a sweep / track control signal generator 7, a phase detector 4 and an up / down counter 51 and an adder / subtractor 52, which constitute a loop filter. It has a ΔF setting circuit 8 ′.

Here, the phase detection circuit 4 receives signals from the A / D converters 10A and 10B and detects the phase deviation of these signals.
The up / down counter 51 increases or decreases the count value based on the up / down control signal from the up / down control unit 50, and the addition / subtraction circuit 52 outputs the count value from the up / down counter 51. ΔF to count value
This is for adding or subtracting ΔF (for the frequency pull-in range) from the setting circuit 8 ′.

Further, the sweep / track control signal generator 7 outputs an INIT signal output from a phase uncertainty removing circuit in an error correction circuit (FEC) for correcting an error in reproduced data (this signal is output when the phase state changes. When the INIT signal is received, a control signal for performing a sweep (Sweep) is input to the up / down control unit 50, and when the INIT signal is not input, a track (Tr) is output.
ack; stop), and inputs a control signal to the up / down control unit 50.
When the sweep control signal is received from the sweep / track control signal generator 7, the up / down counter 51 keeps counting up or down, and when the track control signal is received from the sweep / track control signal generator 7, the phase Up with deviation information from detection circuit 4 /
The up / down control of the down counter 51 is performed.

Further, the .DELTA.F setting circuit 8 'is an up / down counter.
Required range Δ for frequency pull-in to count value from 51
F is added.

The reason why .DELTA.F is given in this way is that only one point can be designated by the count value of the up / down counter 51, so that the frequency cannot be pulled in by the voltage controlled oscillator 6.

With this configuration, for example, when synchronization is lost, the INIT signal is output from the sweep / track control signal generator 7.
Input from the sweep / track control signal generator 7 to the up / down controller.
Entered into 50. As a result, the up / down counter 51
Keeps counting up or counting down,
As a result, the count value goes up or down in one direction.
Then, a required ΔF is added to or subtracted from the counted value, and the voltage-controlled oscillator 6 is controlled with a certain range.
As a result, the phase difference is swept between -45 ° and 45 ° [see FIG. 6 (a)]. And FIG. 6 (b)
As shown in the figure, when the phase difference becomes 0, a track control signal is output from the sweep / track control signal generator 7 this time, so that the up / down controller 50 applies the phase deviation signal from the phase detector 4 to the track control signal. An up / down control signal based on this is output to an up / down counter 51. This allows
The count value of the up / down counter 51 is increased / decreased depending on the up / down control signal, and the phase difference is completely set to 0 (see FIG. 6 (c)).

[Problems to be solved by the invention]

By the way, when handling low transmission speeds, Δ
If F is not made small, cycle skip etc. will increase,
Stable demodulation cannot be expected.

However, if ΔF is small, the point of phase 0 may be passed between the time when the track state is detected and the time when the up / down of the up / down counter 51 is canceled from the one-way control. There is a problem that a sweep state occurs, and it is difficult to shift to a track state, and that the frequency pull-in does not work well.

The present invention has been made in view of such problems,
A Costas loop type demodulator that uses a Costas loop to make the range for frequency acquisition variable and enables easy frequency acquisition and stable demodulation even at low transmission speeds. It is intended to provide a device.

[Means for solving the problem]

 FIG. 1 is a block diagram showing the principle of the present invention.

As shown in FIG. 1, in the case of the present invention as well, each of the input signal lines divided into two systems by the 90 hybrid 1 has a mixer 2A; 2B, and a low-pass filter receiving the output from the mixer 2A; 2B. 3A; 3B, the deviation output between the low-pass filters 3A and 3B is output from the synchronous detection circuit 4, and this deviation output is fed back to the voltage controlled oscillator 6 via the loop filter 5;
This is for a Costas loop type demodulator that inputs the output from the mixer to each of the mixers 2A and 2B.

Reference numeral 7 denotes a sweep / track control signal generator. The sweep / track control signal generator 7 receives a phase state change signal (INIT signal) detected from the demodulated output and output when the phase state changes. And a sweep control signal for setting the voltage controlled oscillator 6 to the sweep mode is output to the loop filter 5, and when the phase change signal is no longer input, the track control signal for setting the voltage controlled oscillator 6 to the track mode is set to the loop filter. 5 out.

Further, reference numeral 8 denotes a frequency pull-in auxiliary unit, which gives a required range ΔF for frequency pull-in to the voltage-controlled oscillator control signal output from the loop filter 5, and this ΔF is variable. I can do it. That is, the frequency pull-in assisting unit 8
Based on the control signal from the sweep / track control signal generator 7, ΔF set by the frequency pull-in assisting unit 8 is:
When the voltage controlled oscillator 6 is in the sweep mode, it is set to be large, and when the voltage controlled oscillator 6 is in the track mode, it is set to be small.

Reference numeral 9 denotes a protection circuit. The protection circuit 9 prohibits the frequency pull-in assisting unit 8 from changing the frequency pull-in range (ΔF) for a predetermined time after the sweep mode is switched to the track mode. In this case, the protection circuit 9 is configured to prohibit the frequency pull-in assisting unit 8 from changing the frequency pull-in range (ΔF) while the phase difference is pulled to a state of 0 after the mode is changed from the sweep mode to the track mode. Is preferred.

(Operation)

With this configuration, for example, when synchronization is lost, the INIT signal is output from the sweep / track control signal generator 7.
Therefore, the sweep control signal is input from the sweep / track control signal generator 7 to the loop filter 5. As a result, the voltage controlled oscillator 6 enters the sweep mode, and sweeps the phase difference between -45 ° and 45 °. At this time, ΔF is set to be large.

Then, when the range including the phase difference 0 is reached, a track control signal is output from the sweep / track control signal generation unit 7, so that the voltage control oscillator 6 releases the sweep mode and outputs the phase deviation signal from the phase detection circuit 4. , The phase difference is completely set to zero. Then, when the phase difference becomes 0 and the synchronization is completed, ΔF is changed to a smaller value than before.

Further, even if the control signal from the sweep / track control signal generator 7 enters the sweep mode, the protection circuit 9 is kept for a while (while the phase difference is completely pulled to the state of 0 after the track state). However, it is prohibited to reduce ΔF. Therefore, even if the track state is entered, if the state shifts again to the sweep state within the time required to reduce ΔF, ΔF is not changed.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a block diagram of a four-phase PSK demodulator employing a Costas loop type demodulation system as one embodiment of the present invention. In the four-phase PSK demodulator shown in FIG.
The QPSK wave in the Hz band is frequency-converted by the frequency conversion circuit in accordance with the signal from the synthesizer, further filtered by the 48 MHz band-pass filter, and the gain is adjusted by the variable attenuator. Are divided into two different signals.

Each signal is input to a carrier reproduction circuit CRC via mixers 2A; 2B, low-pass filters 3A; 3B for band limitation, and A / D converters 10A; 10B.

The carrier recovery circuit CRC has functions of phase detection and a loop filter. The output of the loop filter portion is input to the voltage controlled oscillator (VCO) 6 via the D / A converter 11, and the voltage of the voltage controlled oscillator 6 Output is each mixer 2A, 2B
To be entered.

By the way, this carrier recovery circuit CRC is an up / down control unit that constitutes the phase detection circuit 4 and the loop filter.
50, up / down counter 51, addition / subtraction circuit 52, sweep / track control signal generator 7, ΔF variable circuit
8, a protection circuit 9 is provided.

Here, the phase detection circuit 4, the up / down control section 50, the up / down counter 51, and the addition / subtraction circuit 52 are the same as those of the conventional one, and therefore the description thereof is omitted.

When the sweep / track control signal generator 7 receives the INIT signal (phase state change signal) output from the phase uncertainty removing circuit in the error correction circuit (FEC) for correcting an error in the reproduced data, the sweep / track control signal generator 7 sweeps. A control signal is input to the up / down control unit 50, and a track control signal is input to the up / down control unit 50 when the INIT signal is not input. The results are as shown in FIGS.

Further, the ΔF variable circuit 8 includes an up / down counter
Required range Δ for frequency pull-in to count value from 51
F is added, and the ΔF variable circuit 8 can further change the value of ΔF. That is, the ΔF variable circuit 8 is configured to set the ΔF variable circuit 8 based on the control signal from the sweep / track control signal generator 7.
Is set to be large when the voltage-controlled oscillator 6 is in the sweep mode, and is set to be small when the voltage-controlled oscillator 6 is in the track mode.

Further, even if the control signal from the sweep / track control signal generator 7 enters the sweep mode, the protection circuit 9 continues for a while (while the phase difference is completely pulled into the state of 0 after entering the track state). Is for prohibiting the reduction of ΔF. Therefore, even if the track state is established, if the state shifts to the sweep state again within the time until ΔF is reduced, ΔF is not changed.

Note that when the state shifts to the sweep state after ΔF is reduced, the protection circuit 9 issues an instruction by the ΔF variable circuit 8 to increase ΔF again.

According to the above-described configuration, for example, when the synchronization is lost, the INIT signal is input to the sweep / track control signal generator 7, and the sweep / track control signal is output from the sweep / track control signal generator 7. Control unit 50
Is input to As a result, the up / down counter 51 continues to count up or down, and as a result, the count value increases or decreases in one direction. Then, a required ΔF is added to or subtracted from the counted value, and the voltage-controlled oscillator 6 is controlled with a certain range.
As a result, the phase difference is swept between -45 ° and 45 ° (see FIG. 6 (a)). At this time, ΔF is set to be large.

Then, as shown in FIG. 6 (b), in the range including the phase difference 0, a track control signal is output from the sweep / track control signal generator 7 this time, so that the up / down controller 50 performs phase detection. Up / down counter for up / down control signal based on phase deviation signal from circuit 4
Take out to 51. As a result, the count value of the up / down counter 51 is increased / decreased depending on the up / down control signal, and the phase difference is completely made zero (see FIG. 6 (c)).
Then, the phase difference becomes 0 and the synchronization is completed [not immediately after the track state is detected; see FIG. 3 (a)].
Is changed to a smaller value than before.

Note that when the state shifts to the sweep state after ΔF is reduced, ΔF is set again to a large value by the ΔF variable circuit 8 according to an instruction from the protection circuit 9.

As described above, since ΔF is increased during the sweep, while the track state is detected, while the up / down of the up / down counter 51 is canceled from the one-way control,
Since there is no danger of passing the point of phase 0, the transition to the track state, and eventually the pull-in of the frequency is successful, and after the phase difference becomes 0, ΔF is reduced. Even in the case of handling, stable demodulation can be expected without increasing cycle skip and the like.

〔The invention's effect〕

As described in detail above, according to the Costas loop type demodulation device of the present invention, it should be added to the voltage control oscillator control signal set by the frequency pull-in auxiliary unit based on the control signal from the sweep / track control signal generation unit. The frequency pull-in range is set to be large when the voltage-controlled oscillator is in the sweep mode, and is set to be small when the voltage-controlled oscillator is in the track mode, and after the sweep mode is switched from the sweep mode to the track mode. The predetermined time is provided with a protection circuit for inhibiting the change of the frequency pull-in range in the frequency pull-in auxiliary unit, so that even if the transmission speed is low, the frequency pull-in is easily performed,
In addition, there is an advantage that stable demodulation can be performed.

The protection circuit may be configured to prohibit the frequency pull-in assisting unit from changing the frequency pull-in range while the phase difference is pulled to 0 after the sweep mode is switched to the track mode. In this way, while detecting the track state and releasing the up / down of the up / down counter from the one-way control,
There is an advantage that the possibility of passing the point of phase 0 is eliminated, and stable demodulation becomes possible.

[Brief description of the drawings]

1 is a block diagram showing the principle of the present invention, FIG. 2 is a block diagram showing one embodiment of the present invention, FIG. 3 is a timing chart showing input / output waveforms of a sweep / track control signal generator, and FIG. FIG. 5 is a block diagram showing a conventional example, and FIGS. 6 (a) to 6 (c) are diagrams for explaining a sweep / track control process. In the figure, 1 is a 90-degree hybrid, 2A and 2B are mixers, 3A and 3B are low-pass filters, 4 is a phase detector, 5 is a loop filter, 6 is a voltage controlled oscillator (VCO), and 7 is a sweep / track control signal. 8 is a ΔF variable circuit (frequency pull-in auxiliary unit), 9 is a protection circuit, 10A and 10B are A / D converters, 11 is a D / A converter, 20 is a synthesizer, 21 is a frequency conversion circuit, and 22 is a band. A pass filter, 23 is a variable attenuator, 24 is a bit timing recovery (clock recovery circuit), 50 is an up / down control unit, 51 is an up / down counter, 52 is an addition / subtraction circuit, and CRC is a carrier recovery circuit.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04L 27/22 H03L 7/12

Claims (2)

(57) [Claims] An input signal line divided into two systems includes a mixer and a low-pass filter receiving an output from the mixer, and outputs a deviation output between the low-pass filters via a loop filter to a voltage-controlled oscillator. In the Costas loop type demodulator that feeds back the output from the voltage controlled oscillator to each mixer, when a phase state change signal detected from the demodulated output and output when the phase state changes is input, A sweep control signal for setting the voltage controlled oscillator to the sweep mode is output to the loop filter. When the phase state change signal is not input, a track control signal for setting the voltage controlled oscillator to the track mode is output to the loop filter. A sweep / track control signal generating section to output, and a voltage output from the loop filter. A frequency pull-in auxiliary unit for providing a required range for frequency pull-in to the control oscillator control signal, wherein the frequency pull-in auxiliary unit performs the frequency pull-in based on a control signal from the sweep / track control signal generating unit. The frequency pull-in range to be added to the voltage-controlled oscillator control signal set by the auxiliary unit is set to be large when the voltage-controlled oscillator is in the sweep mode, and is set to be small when the voltage-controlled oscillator is in the track mode. And a protection circuit for prohibiting a change in a frequency pull-in range in the frequency pull-in assisting unit for a predetermined time after the sweep mode is switched to the track mode. Type demodulator. 2. The protection circuit according to claim 1, wherein said protection circuit inhibits the frequency pull-in assisting unit from changing the frequency pull-in range while the phase difference is pulled to 0 after the sweep mode is switched to the track mode. 2. The Costas loop type demodulator according to claim 1, wherein: