JPH0669972A - Frequency sweep circuit - Google Patents

Abstract

PURPOSE:To shorten the synchronization time for a carrier and to reduce ineffective portions by detecting a difference between a carrier frequency of an input signal and a frequency of a local oscillation signal so as to compare the level, discriminating a direction in which the frequency sweep is started and setting the direction. CONSTITUTION:A complex multiplier section 1 is provided with a complex multiplier 9 and a numerically controlled oscillator 10, and a carrier recovery section 3 is provided with a sweep wave generating section 14 generating a sweep wave, a synchronization detection section 17 receiving an output of the complex multiplier 9 and detecting the synchronization, and a changeover device 11 selecting an output from the sweep wave generating section 14 or an output from the complex multiplier 9 according to the detection signal from the synchronization detection section 17 and through which the selected output is given to the numerically controlled oscillator 10 generating a local oscillating signal 10. In this case, a frequency error detection section 16 detects the frequency or phase difference of the input signal carrier and the local oscillating signal to compare the quantity. Moreover, a sweep direction control section 13 discriminates and sets a direction in which the frequency sweep is started according to the comparison information from the frequency error detector 16.

Description

Detailed Description of the Invention

[0001]

The present invention is used for frequency sweeping after carrier recovery. In particular, it is used for frequency sweep for expanding the capture range of the phase locked loop. The present invention relates to a frequency sweep circuit capable of shortening carrier synchronization time.

[0002]

2. Description of the Related Art A conventional frequency sweep method has been to detect a synchronous state in a phase locked loop circuit and always start sweeping the frequency of a local oscillation signal in a fixed direction only in the asynchronous state.

Here, the details of the prior art will be described with reference to BPSK.
(Binary Phase Shift Keying) A carrier synchronization circuit for a modulated signal will be described as an example.

First, when the phase locked loop is in a synchronized state, the signal diagram (phase locus) on the complex plane (hereinafter referred to as PQ plane) of the demodulated signal is near points A and B as shown in FIG. concentrate. Further, when the phase locked loop circuit shifts to the asynchronous state, the phase locus is dispersed on the circumference as shown in FIG.

Therefore, in order to detect the synchronization state, such a property is utilized, and the existence probability in the vicinity of points A and B of the phase locus of the demodulated signal is compared with a certain threshold value (hatched area in FIG. 7). As a result of this detection, in the case of an asynchronous state, the frequency of the local oscillator signal is adjusted to keep the difference between the carrier frequency of the input modulation signal and the frequency of the internal local oscillator signal within the acquisition frequency range of the phase locked loop. Sweep
Then, when it was detected that the error frequency was within the capture frequency range, the sweep was ended and the synchronization state was established.

[0006]

In such a conventional frequency sweep method, when the frequency shifts to an asynchronous state, the frequency of the local oscillator signal is always swept from a fixed direction, so that the center frequency of the local oscillator signal is When the carrier frequency of the input signal exists in the direction opposite to the sweep start direction, more than half of the sweep time becomes invalid.

The present invention solves such a problem and provides a circuit capable of reducing an invalid portion of the sweep time which occurs when the carrier frequency of the input signal exists in the direction opposite to the sweep start direction. The purpose is to

[0008]

According to the present invention, a carrier wave reproducing section generates a sweep wave, a sweep wave generating section, a sync detecting section for inputting an output of a multiplier to detect sync, and a sync detecting section of the sync detecting section. In a frequency sweep circuit including a switch for switching between an output from the sweep wave generator and an output from the multiplier according to a detection signal and outputting the output to a numerically controlled oscillator that generates a local oscillation signal, an input signal carrier and the local It includes an error detector that detects the frequency or phase difference from the oscillation signal and compares the high and low, and a sweep direction control unit that determines and sets the direction to start frequency sweep according to the comparison information of this detector. Characterize.

[0009]

[Operation] When the sweep is started when the synchronous state is changed to the asynchronous state or when the power is turned on,
The difference between the carrier frequency of the input signal and the frequency of the local oscillation signal is detected to compare the levels, and the direction in which the frequency sweep is started is determined and set based on this comparison information.

As a result, the carrier synchronization time is shortened,
The ineffective part of the sweep time can be reduced.

[0011]

Embodiments of the present invention will now be described with reference to the drawings. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG.
FIG. 6 is a diagram showing state transitions in the embodiment of the present invention.

In the embodiment of the present invention, a complex multiplication unit 1 for performing complex multiplication, a clock reproduction unit 2 for reproducing an output clock signal by taking in the output of the complex multiplication unit 1, and a carrier wave reproduction unit 3 for reproducing a carrier wave. And the complex multiplier 1 includes the complex multiplier 9 and the numerically controlled oscillator 10, and the carrier recovery unit 3 inputs the sweep wave generator 14 for generating a sweep wave and the output of the complex multiplier 9 for synchronization. Synchronization detector 17 for detecting
And a switcher 11 for switching the output from the sweep wave generator 14 and the output from the complex multiplier 9 according to the detection signal of the synchronization detector 17 and outputting the output to the numerically controlled oscillator 10 for generating a local oscillation signal. Further, as a feature of the present invention, a frequency (phase) error detector 16 for detecting the frequency or phase difference between the input signal carrier and the local oscillation signal to compare the high and low, and the frequency (phase) error detector 16 And a sweep direction control unit 13 that determines and sets the direction in which the frequency sweep is started in accordance with the comparison information.

The present embodiment shows an example of the configuration in the case of using a DSP (dynamic support program).

When the BPSK digital modulation signal is input to the complex multiplication unit 1, the level is adjusted by the information fed back from the carrier wave reproduction unit 3 and then the frequency is swept by the information fed back in the same manner (still in the synchronized state). In this case, frequency (phase) correction is performed based on the frequency (phase) error information obtained by the following calculation).

The feedback information for performing this frequency sweep is generated by the carrier wave reproducing section 3 as follows.

First, when the real part of the reproduction data is represented by P and the imaginary part is represented by Q, the P and Q can be represented as follows.

P = A * cos (aπ + α) Q = A * sin (aπ + α) α is an error between the carrier frequency of the input signal and the frequency (phase) of the local oscillation signal, a = 0 or 1, P ² + Q ² = 1 When the level is adjusted so that A becomes 1. P
By forming a Costas loop of * Q, P * Q = cos (aπ + α) * sin (aπ + α) = (1/2) sin (2aπ + 2α) = (1/2) sin (2α) is obtained. The phase synchronization information is obtained from the value of this equation (when in the phase synchronization state, this signal is supplied to the complex multiplication unit 1 as a frequency (phase) error signal after passing through the loop filter to control the phase rotation amount. To correct the frequency (phase).

Here, the P and Q signals of the reproduction data at the time t = t _n after the transition from the synchronous state to the asynchronous state are expressed as (P, Q) = (P _n , Q _n ) = (cos (a _n π + α _n ), sin (a _n π + α _n )) ... Similarly, the P and Q signals of the reproduced data at time t = t _{n + 1} are (P, Q) = (P _{n + 1} , Q _{n + 1} ) = (cos (a _{n + 1} π + α _{n + 1).} , Sin (a _{n + 1} π + α _{n + 1} )) ... And Δt = t _{n + 1} −t _n represents the sampling period of the reproduction data, the signal strength is S = sin (α _{n + 1−} α _n ) = Q _{n + 1} * P _n −P _{n + 1} * Q _n . Assuming that the relationship between S and (α _{n + 1} −α _n ) is −π <α _{n + 1} −α _n <π as shown in FIG. 3, the frequency (phase) detected at a certain time t _n . to error alpha _n, if the case the phase error alpha _{n + 1} detected in the following sample data is large S> 0, and the small conversely becomes S <0.

When shifting from the synchronous state to the asynchronous state,
The error frequency between the carrier frequency of the input signal and the frequency of the local oscillator signal is considered to have a characteristic of monotonically increasing or monotonically decreasing with time in the normal case. Therefore, when the value of S is positive, Therefore, when the value of S is negative, the frequency sweep is started from the positive direction. Such a state in the frequency sweep direction is shown in FIGS. 4 (a) and 4 (b).

[0020]

As described above, according to the present invention, when the frequency is swept when the synchronous state is changed to the asynchronous state, the frequency of the modulation signal deviates from the frequency of the local oscillation signal to either positive or negative. Since the frequency sweep can be performed from either the negative direction or the positive direction according to the detected information, there is an effect that the frequency sweep time can be validated.

Particularly, in the case of a digital circuit configuration, it can be realized by simple software, and in the usual case, there is an advantage that it can be realized without increasing hardware (power consumption, increase in circuit scale, etc.). is there.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing state transitions in the embodiment of the present invention.

FIG. 3 is a diagram showing a frequency (phase) error according to the embodiment of the present invention.

4A and 4B are views for explaining the frequency sweep direction in the embodiment of the present invention.

FIG. 5 is a diagram showing a coordinate display position of a (P, Q) signal in a synchronized state in a conventional example.

FIG. 6 is a diagram showing coordinate display positions of (P, Q) signals in an asynchronous state in a conventional example.

FIG. 7 is a diagram showing a capture range in a conventional example.

[Explanation of symbols]

 1 Complex Multiplying Unit 2 Clock Reproducing Unit 3 Carrier Regenerating Unit 4 Modulation Signal Input Terminal (Real Part) 5 Modulation Signal Input Terminal (Imaginary Part) 6 Reproduction Data Output Terminal (Pch) 7 Reproduction Data Output Terminal (Qch) 8 Reproduction Clock Output Terminal 9 Complex multiplier 10 Numerically controlled oscillator 11 Switcher 13 Sweep direction controller 14 Sweep wave generator 15 Loop filter 16 Frequency (phase) error detector 17 Sync detector

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display area H04L 7/033

Claims (1)

[Claims] 1. A carrier wave reproducing section, a sweep wave generating section for generating a sweep wave, a sync detecting section for inputting an output of a multiplier to detect synchronization, and a sweep wave generating section according to a detection signal of the sync detecting section. In the frequency sweep circuit including a switch for switching the output from the output section and the output from the multiplier to a numerically controlled oscillator that generates a local oscillation signal, the frequency or phase difference between the input signal carrier and the local oscillation signal. A frequency sweep circuit, comprising: an error detector that detects a difference between high and low and a sweep direction control unit that determines and sets a direction in which a frequency sweep is started according to comparison information of the detector.