JPH0834487B2 - Costas loop demodulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Table of Contents] Industrial field of application Conventional technology [Figs. 5 to 8] Problems to be solved by the invention Means for solving the problems (Fig. 1) Operation (Fig. 1) Embodiments (FIGS. 2 to 4) Effects of the invention [Outline] A Costas loop demodulator for producing carrier wave recovery or lock wave reproduction based on baseband data, in which a range for frequency pulling can be made variable. In addition, the number of protection stages in the protection circuit can also be made variable, so that even when the transmission speed is low, frequency lock and carrier lock can be held easily and quickly, enabling more stable demodulation. In the sweep state, the frequency pull-in range to be added to the voltage-controlled oscillator control signal set by the frequency pull-in auxiliary section is Set to a small value in the track state, and set the number of protection steps to determine the transition from the sweep state to the track state or from the track state to the sweep state set by the protection circuit. It is configured so that it can be changed between the state and the track state.

[Industrial applications]

The present invention relates to a Costas loop type demodulator that produces carrier wave reproduction or clock reproduction based on baseband data.

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

[Conventional technology]

Fig. 5 shows four phases that adopt the conventional Costas loop type demodulation method.
Although it is a block diagram of the PSK demodulator, in the 4-phase PSK demodulator shown in FIG. 5, for example, a QPSK wave in the 70 MHz band is frequency-converted by the frequency conversion circuit 21 in accordance with the signal from the synthesizer 20, and further 48 MHz. After being filtered by the bandpass filter 22 and adjusted in gain by the variable attenuator 23,
The 90 ° hybrid 1 splits the signal into two systems with different 90 ° phases.

Then, each signal is input to the carrier reproducing circuit CRC via the mixers 2A; 2B, band-passing low-pass filters 3A; 3B and A / D converters 10A; 10B.

The carrier recovery circuit CRC has the functions of phase detection and a loop filter, and 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 controlled oscillator 6 Output is each mixer 2A, 2B
To be entered.

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

By the way, as shown in FIG. 6, the carrier reproduction circuit CRC includes a sweep / track control signal generator 7, as well as an up / down counter 51 and an addition / subtraction circuit 52 which constitute a phase detection circuit 4 and a loop filter. It has a ΔF setting circuit 8 '.

Here, the phase detection circuit 4 receives the signals from the A / D converters 10A and 10B and detects the phase deviation of these signals.
The up / down counter 51 counts up (Up) or down (Down) 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 for the count value
It is for adding or subtracting ΔF (frequency pull-in range) from the setting circuit 8 '.

In addition, the sweep / track control signal generator 7 outputs the INIT signal (this signal is issued when the phase state changes) from the phase uncertainty removing circuit in the error correction circuit (FEC) that corrects the error in the reproduced data. When a phase change signal is received), a control signal for performing a sweep is input to the up / down controller 50, and when the INIT signal is not input, the track (Tr
The control signal for ack; (stop sweep) is input 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 detection is performed. The deviation information from the circuit 4 is used to control up / down of the up / down counter 51.

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

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

With such a configuration, if the synchronization is lost, for example, the INIT signal is output to the sweep / track control signal generator 7.
The sweep control signal from the sweep / track control signal generator 7 is input to the up / down control unit.
Entered into 50. As a result, the up / down counter 51
Keeps counting up or down,
As a result, the count value goes up or down in one direction.
Then, the required ΔF is added to or subtracted from this count value to give a certain range to control the voltage controlled oscillator 6.
As a result, the phase difference is swept between −45 ° and 45 ° [see FIG. 7 (a)]. And FIG. 7 (b)
As shown in, when the phase difference is in the range including 0, the sweep / track control signal generator 7 outputs the track control signal this time, so the up / down controller 50 outputs the phase deviation signal from the phase detection circuit 4. An up / down control signal based on this is output to the up / down counter 51. This allows
The count value of the up / down counter 51 goes up / down depending on the up / down control signal to completely set the phase difference to 0 [see FIG. 7 (c)].

[Problems to be Solved by the Invention]

By the way, when dealing with low transmission speed,
If you do not make F small, cycle skips will increase,
We cannot expect stable demodulation.

However, if ΔF is small, there is a possibility that the point of phase 0 may be passed while the up / down counter 51 is released from the up / down control from the one-way control after the track state is detected. In this case, again. There is a problem that it becomes a sweep state, it is difficult to transition to the track state, and eventually the frequency pulling does not work well.

Therefore, as shown in FIG. 8, in the Costas loop type, a ΔF setting circuit 8 capable of varying the range ΔF for frequency pull-in is provided, and the transition from the sweep state to the track state and from the track state are performed. Number of protection stages (eg IN
By setting the number of IT signal inputs and the required delay time) and providing a protection circuit 9'that provides a certain degree of protection for the sweep / track control signal, it is possible to easily pull in the frequency even when the transmission speed is low. It is also possible to do so.

A timing chart of input / output signals to / from the sweep / track control signal generator 7 in this case is
It becomes like (a)-(c) of FIG.

Further, in FIG. 8, the same reference numerals as those in FIGS. 6 and 7 indicate almost the same parts.

However, in this case, since the number of protection stages in the protection circuit 9'is constant, there are the following problems. In other words, even if you move from the sweep state to the track state,
Low C / N (carrier / noise) even if the carrier cannot be tracked or conversely is in the track state
At times, the carrier cannot be pulled in and held.

The present invention has been made in view of such a problem, and enables to change the range for frequency pull-in in the one using the Costas loop and also to change the number of protection stages in the protection circuit. It is an object of the present invention to provide a Costas loop demodulation device that can easily and quickly perform frequency pull-in and carrier pull-in and hold, even when the transmission speed is low, to enable more stable demodulation. .

[Means for solving the problem]

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

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

Reference numeral 7 denotes a sweep / track control signal generating unit. The sweep / track control signal generating unit 7 sets a sweep control signal for setting the voltage controlled oscillator 6 in the sweep mode and for setting the voltage controlled oscillator 6 in the track mode. The track control signals are output to the loop filters 5, respectively.

Further, 8 is a frequency pull-in assisting section, and this frequency pull-in assisting section 8 gives a required range ΔF for frequency pull-in to the voltage controlled oscillator control signal output from the loop filter 5, and ΔF can be varied. It is like this. That is, the frequency pull-in assisting unit 8 sets the frequency pull-in range ΔF to be added to the voltage controlled oscillator control signal set by the frequency pull-in assisting unit 8 large in the sweep state and small in the track state. It is configured to set.

Reference numeral 9 is a protection circuit, which sets the number of protection stages for determining the transition from the sweep state to the track state or the transition from the track state to the sweep state. It is configured to change the number of protection steps depending on when the track state is set and when the track state is set.

[Action]

With such a configuration, for example, when the synchronization is lost, the sweep / track control signal generator 7 inputs the sweep control signal to the loop filter 5. As a result, the voltage controlled oscillator 6 enters the sweep mode, and the phase difference shift sweeps between -45 ° and 45 °. At this time, ΔF is set to be large and the number of protection steps is set to a predetermined value suitable for the sweep state.

Then, in the range including the phase difference 0, the track control signal is output from the sweep / track control signal generation unit 7 in the future, so the voltage controlled 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 0 based on. Then, when the phase difference becomes 0 and the synchronization is completed, ΔF is changed to a smaller value than before. Further, at this time, the number of protection stages set in the protection circuit 9 is set to a value different from that in the above-mentioned sweep state.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram of a 4-phase PSK demodulator adopting the Costas loop type demodulation system as one embodiment of the present invention. In the 4-phase PSK demodulator shown in FIG.
The QPSK wave in the Hz band is frequency-converted by the frequency conversion circuit according to the signal from the synthesizer, further filtered by the 48MHz bandpass filter, and the gain is adjusted by the variable attenuator, then 90 ° hybrid 1 and 90 ° phase Signal of two different systems.

Then, each signal is input to the carrier reproducing circuit CRC via the mixers 2A; 2B, band-passing low-pass filters 3A; 3B and A / D converters 10A; 10B.

The carrier recovery circuit CRC has the functions of phase detection and a loop filter, and 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 controlled oscillator 6 Output is each mixer 2A, 2B
To be entered.

By the way, in addition to the phase detection circuit 4, the sweep / track control signal generator 7 or the up / down controller 50, the up / down counter 51, and the adder / subtractor 52, which constitute the loop filter, the carrier reproducing circuit CRC is It has a ΔF variable circuit 8 as a frequency pull-in correction unit and a protection stage number variable circuit 9 as a protection circuit.

Here, the phase detection circuit 4, the sweep / track control signal generation unit 7, the up / down control unit 50, the up / down counter 51, and the addition / subtraction circuit 52 are the same as the conventional ones, and therefore their explanations are omitted. .

Here, the ΔF variable circuit 8 is an up / down counter.
Required range for frequency pull-in to the count value from 51 Δ
Although the value of F is added, the ΔF variable circuit 8 can further change the value of ΔF. That is, the ΔF variable circuit 8 is configured so that ΔF set by the ΔF variable circuit 8 is set large in the sweep state and set small in the track state.

Further, the protection stage variable circuit 9 includes a protection stage number for determining the transition from the sweep state to the track state (this protection stage number is referred to as a front protection stage number) and a protection stage number for determining the transition from the track state to the sweep state (this protection stage number). The number of protection stages is set as the number of rear protection stages), and the protection stage number varying circuit 9 is configured so that the number of protection stages can be changed between the sweep state and the track state. For example, in the sweep state, the number of front and rear protection stages is set to a small (small) value, and in the track state, it is set to a large (large) value (optimal value) larger than that in the sweep state. In this way, if the number of front and rear protection stages is reduced in the sweep state, it is possible to quickly detect the transition from the sweep state to the track state, and if the number of rear protection stages is small, the track state is detected by an error. However, you can quickly return to the sweep state.

The number of protection stages includes the number of front protection stages and the number of rear protection stages as described above. First, the number of front protection stages is changed from the asynchronous state (sweep state) to the synchronous state (track state).
If the synchronization information is detected a plurality of times in succession when shifting to, that is, if the required time INIT signal does not exist, the number of stages set to determine the synchronization (the synchronization information is continuously detected. The number of times or time), and if you set this number of forward protection steps to a small number, when accidentally detecting synchronization,
On the other hand, if the number of forward protection steps is set to a large number while the sweep is stopped, the sweep cannot be stopped when the synchronization is really synchronized. Therefore, it is preferable that the number of front protection stages is set small when asynchronous and large when synchronous. In addition, the backward protection stage number means that when the synchronous state (track state) shifts to the asynchronous state (sweep state), the synchronous information is not detected a plurality of times consecutively.
That is, when the required time INIT signal is present, it is the number of stages (the number of times or the number of times when asynchronous information is not detected continuously) that is set to determine that it is asynchronous. However, if a large number of rear protection stages are set, it will be difficult to switch to the sweep if the backward protection stage is set to a large number. Therefore, it is preferable that the number of backward protection stages is also set small when asynchronous and large when synchronizing.

Next, FIG. 3 shows a configuration example for changing the number of protection steps and ΔF. In FIG. 3, reference numeral 91 denotes a control circuit, which receives a phase state change signal (INIT signal) issued when the phase state is detected from the demodulation output and also sends an INIT CAR (carrier) signal. By receiving as a clock, the presence / absence information of the INIT signal is output.

Reference numeral 92 denotes a front protection stage number setting down counter, which receives the presence / absence information of the INIT signal from the control circuit 91, and when the INIT signal is present, continues to load the value of the front protection stage number, When the INIT signal no longer exists, it starts counting down and outputs a track state signal.

93 is a down counter for setting the number of backward protection stages. This down counter 93 receives the presence / absence information of the INIT signal from the control circuit 91 and loads the value of the number of backward protection stages when the INIT signal does not exist. Continuing, when the INIT signal comes to exist, it starts counting down and outputs the signal in the sweep state.

Reference numeral 94 denotes a set / reset circuit. The set / reset circuit 94 is set / reset by outputs from the front protection stage number setting down counter 92 and the rear protection stage number setting down counter 93.

Reference numeral 95 denotes a counter. The counter 95 receives the output from the set / reset circuit 94 and also receives the INIT CAR signal as a clock to be reset in the sweep state, and outputs the initial value to be in the track state. Then, counting is started, and the output of the counter 95 is output to the ROM 96 described later as address information. The counter 95 provides the sweep / track control signal generator 7 with the carry-out signal as to whether the track mode or the sweep mode should be selected.

96 is a ROM. This ROM96 has a setting value for the number of front protection stages,
A plurality of sets of the set value of the rear protection step number and the set value of ΔF are stored, and the set information of the set value of the front protection step number, the set value of the rear protection step number and the set value of ΔF is stored by the address information from the counter 95. One of them is selected and supplied to the front protection stage number setting down counter 92, the rear protection stage number setting down counter 93 and the ΔF setting circuit 8.

That is, the control circuit 91, the front protection stage number setting down counter 92, the rear protection stage number setting down counter 93,
The set / reset circuit 94, the counter 95, and the ROM 96 set the number of protection steps to determine the transition from the sweep state to the track state or the transition from the track state to the sweep state. Constitutes a protection circuit 9 for changing the number of protection stages.

Further, the counter 95 and the ROM 96, together with the ΔF variable circuit 8, add a required range ΔF for frequency pulling to the voltage controlled oscillator control signal output from the loop filter 5, and the frequency pulling range ΔF A frequency pull-in auxiliary unit is set to a large value in the sweep state and a small value in the track state.

The timing relationship between the INIT CAR signal and the INIT signal is shown in FIGS. 4 (a) and 4 (b).

With the above configuration, for example, when the synchronization is lost, the sweep / track control signal generator 7 inputs the sweep control signal to the up / down controller 50. As a result, the up / down counter 51 continues to count up or count down, and as a result, the count value counts up or down in one direction. Then, the required ΔF is added to or subtracted from this count value to give a certain range to control the voltage controlled oscillator 6. As a result, the phase difference is swept between −45 ° and 45 ° [see FIG. 7 (a)]. At this time, ΔF is set to be large, and the number of front and rear protection steps is set to be small.

Then, as shown in FIG. 7 (b), the range including the phase difference 0 [in the state shown in FIG. 7 (b), the number of protection steps is still set small], and this time the sweep / track is executed. Since the track control signal is output from the control signal generator 7, the up / down controller 50 uses the phase detection circuit 4
The up / down control signal based on the phase deviation signal from is output to the up / down counter 51. By this /
The count value of the down counter 51 goes up / down depending on the up / down control signal to completely set the phase difference to 0 [see FIG. 7 (c)].

After that, when the phase difference becomes 0 and the synchronization is completed [not immediately after the track state is detected, but after a short delay (this delay time is set by the counter 95)], the counter 95
According to the address instruction from, the reading ΔF of the ROM 96 changes, and as a result, ΔF is changed to a smaller value than before. Further, the set values of the front protection stage number and the rear protection stage number can be changed from the small value up to now to the optimum value of the large value.

It should be noted that when the state is changed to the sweep state again after reducing ΔF, it is returned to the original state by the instruction of the protection stage number varying circuit 9. That is, ΔF is set to a large value again, and the set values of the front protection stage number and the rear protection stage number are also returned to the small values.

In this way, since ΔF is increased while reducing the number of protection steps during the sweep, the transition from the sweep state to the track state can be detected early, and further, after the track state is detected early as described above. There is no possibility that the point of phase 0 will be passed while the up / down of the up / down counter 51 is released from the one-way control, whereby the transition to the track state, and hence the frequency pull-in can be performed quickly and surely. be able to. Also,
After the phase difference becomes 0, ΔF is reduced and the number of protection steps is increased to restore the optimum value. Therefore, even when handling a low transmission rate, cycle skips do not increase. Very stable demodulation can be expected.

The variable protection stage number circuit 9 may be provided between the sweep / track control signal generator 7 and the ΔF variable circuit 8. In addition, in some cases, the number of protection stages is increased during the sweep, and when the track state is reached. It is also possible to reduce the number of protection steps.

〔The invention's effect〕

As described in detail above, according to the Costas loop demodulator of the present invention, the frequency pull-in range to be added to the voltage-controlled oscillator control signal is set large in the sweep state and set small in the track state. Since it is configured so that the number of protection steps can be changed between the sweep state and the track state, frequency pulling and carrier pulling hold can be performed easily and quickly even when the transmission speed is low. There is an advantage that it is possible to perform stable demodulation.

[Brief description of drawings]

1 is a block diagram showing the principle of the present invention, FIG. 2 is a block diagram showing an embodiment of the present invention, FIG. 3 is a block diagram showing a configuration example for changing the number of protection stages, and FIG. 4 is FIG. 5 is a timing chart showing the relationship between the INIT signal and the INIT CAR signal used in FIG. 5, FIG. 5 is a block diagram of a 4-phase PSK demodulator, FIG. 6 is a block diagram showing a conventional example, and FIGS. ) Is a diagram for explaining the sweep / track control process, FIG. 8 is a block diagram of the one devised in the process of devising the present invention, and FIG. 9 is a timing chart showing input / output waveforms of the sweep / track control signal generator. . In the figure, 1 is a 90 ° hybrid, 2A and 2A are mixers, 3A and 3B are low pass filters, 4 is a phase detection circuit, 5 is a loop filter, 6 is a voltage controlled oscillator (VCO), and 7 is a sweep / track control signal generation. Section, 8 is a ΔF variable circuit (frequency pulling auxiliary section), 9 is a protection stage number variable circuit (protection circuit), 10A,
10B is an A / D converter, 11 is a D / A converter, 20 is a synthesizer, 21 is a frequency conversion circuit, 22 is a bandpass 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, 91 is a control circuit, 92 is a down counter for setting the number of forward protection stages, 93
Is a down counter for setting the number of backward protection stages, 94 is a set / reset circuit, 95 is a counter, 96 is ROM, and CRC is a carrier reproducing circuit.

Claims (1)

[Claims] 1. A mixer (2A; 2B) and a low-pass filter (3A; 3B) for receiving an output from the mixer (2A; 2B) are provided for each of the input signal lines divided into two systems, The deviation output between the low pass filters (3A, 3B) is fed back to the voltage controlled oscillator (6) via the loop filter (5), and the output from the voltage controlled oscillator (6) is fed to each mixer (2A, 2B). In the Costas loop demodulator input to the loop filter (1), a sweep control signal for setting the voltage controlled oscillator (6) in the sweep mode and a track control signal for setting the voltage controlled oscillator (6) in the track mode are respectively provided. 5) a sweep / track control signal generator (7), and a required range for pulling the frequency into the voltage controlled oscillator control signal output from the loop filter (5). ΔF)
And a protection circuit (9) for setting the number of protection stages for determining the transition from the sweep state to the track state or the transition from the track state to the sweep state. The pull-in assisting unit (8) is configured to set the frequency pull-in range (ΔF) to be added to the voltage controlled oscillator control signal to a large value in the sweep state and a small value in the track state, and A Costas loop demodulator, wherein the protection circuit (9) is configured so that the number of protection stages can be changed between a sweep state and a track state.