JPS6188636A - Demodulation circuit - Google Patents

Abstract

PURPOSE:To secure the stable demodulation with a both-side band wave signal having suppressed carrier wave by providing a reference oscillator equivalent to an intermediate frequency and detecting the difference of phase between the intermediate frequency and an input frequency by a COSTAS loop system to feed said phase difference back to a local oscillator together with a loop filter. CONSTITUTION:The signal applied to an input terminal 1 is converted into the 2nd intermediate frequency and supplied to the 1st and 2nd phase detectors 7 and 8 via a band pass filter 6 for comparison with the output of a reference oscillator 9 and a signal underwent a 90 deg. phase shift through a 90 deg. phase shifter 10 respectively. The output of both detectors 7 and 8 are added to a multiplier 19 for execution of multiplication, and the output of this multiplication is fed back to the 2nd local oscillator 4 via a loop filter 18. As a result, the 2nd intermediate frequency is used to the oscillator 9 to secure the stable characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application] The present invention relates to a demodulation circuit, and particularly to a circuit that stably generates an intermediate frequency when demodulating a carrier-suppressed inner band signal.

[Background of the invention]

As described in Japanese Patent Application Laid-Open No. 58-197944, the conventional device can regenerate a carrier wave for coherent detection even in a transmission system in which the carrier wave frequency fluctuates widely. Furthermore, JP-A-5
In No. 8-156160-55, the synchronous detection frequency and phase are tracked to prevent deterioration of the error rate of the reproduced signal. However, with respect to the drift of the intermediate frequency due to the drift of the station S excavator, as in the case of a heterodyne receiver, no consideration has been given to the excess or deficiency of the starvation band wave caused by the bandpass filter for passing the intermediate frequency, which is fixed at 0.degree.

[Purpose of the invention]

An object of the present invention is to provide a demodulation circuit w5 for a heterodyne reception system that stably demodulates carrier-suppressed double-side band signals such as two-phase or four-phase phase shift keying.

[Summary of the invention]

The present invention installs a reference oscillator corresponding to the intermediate Jta wave number, detects the phase difference with the input frequency using the Costas loop method, and uses the loop filter to generate 'M!' to the local oscillator. By stabilizing the intermediate frequency.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. This figure uses a two-electric heterodyne system with two intermediate frequencies to reduce the number of carriers mi.

This is an example of demodulating a four-phase phase shift key ink signal. 1 is an input terminal, 2 is a local oscillator of 1, 3 is a first mixer, and 4 is a second local oscillator.

5 is an N2 mixer, and 6 is a band pass filter.

7 is a first phase detector, and 8 is a second phase detector.

9 is the reference oscillator, 10 is the 90° phase shifter, and 11 is the part 1!
f4JE times N, 12 tX 2nd no'14j foot times M
, 15k? 14 is the second modulation output, 15 is the first multiplier, 16 is the N2 multiplier, 17
is a subtracter, and 18 is a loop filter. A signal applied to an input terminal 1 and a bulky wJ part oscillator 2 are beat down using a first mixer 3 to produce a first intermediate frequency. The temporary intermediate station of E1 and the second station SG shaker 4 are beat down using the second mixer 5: they are made into a second temporary intermediate station.

A bandpass filter 6 removes undesirable out-of-band noise, interference, etc., and performs waveform equalization to make the characteristics of the transmission path transparent. The output is added to the phase detector 7 of Shima 1 and the phase detector 8 of Shima 2, and the phase of the reference oscillator 9 and its output are passed through a 90° phase shifted oscillator 10, and a signal with a phase shift of 90' is 0. The signals are synchronously detected and converted to base band Jj4fc at a phase of 0° and a phase of 90°, respectively. These signals are added to 1 or 7% by -1 by the group 1 judgment circuit 11 and the group 2 judgment circuit 12, and are outputted as 21-digit digital signals to the N1 demodulation output 13 and the second demodulation output 13, respectively. Output 14
get to. . - 10,000, phase 1 @ output of 1fL device 7 and joint 2
′ and the output of the foot circuit 12 to the first multiplication 615,
The output is used as one input of the subtracter 17, the output of the 1-tail 2 phase detector & 17 is the other input. The output of the subtracter 17 is passed through a loop filter 18 and fed back to the local oscillator 4 of Hatake 2. Ding nawachijI! 1
Nooridon bowl 15. Multiplier 16, subtracter 17 and loop filter 18 of patient 2 calculate the phase difference between 8m and the output of reference oscillator 9 in N2 which is the first phase detector 7 and the phase of fringe 2 @ wave number 80 input. A negative feedback loop 1 is constructed to detect and control the E4 part oscillator 4 of N2 and make the phase difference between the output of the second intermediate rI4J oscillator and the base oscillator 9 a certain value. be. Phase difference detection operation is tri-opening 58-1979
Since it is carried by No. 44, it will be omitted here. If an oscillator with good frequency stability, such as a crystal shaft oscillator, is used as the reference oscillator 9, the frequency of the intermediate frequency of Recommendation 2 will be a stable value due to the negative feedback looseness described above, and the frequency of the first local oscillator 2 will change due to temperature fluctuations. Even if it drifts, the frequency of the brown 2 intermediate station wave remains constant, and only a deviation from the center frequency of the bandpass filter 6 occurs, making it possible to obtain stable characteristics.

Furthermore, whether the g-mitter effect is sufficient for one of the inputs of the Roux multiplier 15 and the Straw 2nd multiplier 16 is determined by the judgment circuit 1
The signals from the output of the first phase detection circuit 1 and the output of the second discrimination circuit 12 perform the same operation on the outputs of the first phase detection circuit and the second phase detection circuit.

Another embodiment of the present invention and an implementation for demodulating a L° C., two-phase phase shift key ink signal are shown in FIG. 2. The same reference numerals as in FIG. 1 indicate the same rudders.

19 is a multiplier. The signal given to input terminal 1 is converted to an intermediate frequency of 2, and is passed through a bad pass filter 6 to the output of the reference oscillator 9 and 90° phase shift number 10 is 90
The phase is compared with the phase-shifted signal, and the outputs of the first phase detector 8 and the second phase detector 9 are added to the multiplier 19 for multiplication, and this output is passed through the loop filter 18 to the ″′
C is fed back to the second local oscillator 4. Since the frequency of the second intermediate frequency is essentially the frequency of the reference shaft vibrator 90, stable characteristics can be obtained.

Note that one of the inputs of the multiplier 19 is the output of the phase incubator 7 of ml, but the same operation and effect can also be obtained with the output of the first phase incubator 7 instead.

[Hatsuho's moving bed]

The present invention has the advantage of making it possible to stabilize the intermediate frequency up to heterodyne reception, thereby enabling inexpensive L baseband demodulation without causing excess or deficiency of sidebands due to the bandpass filter.

Furthermore, the intermediate frequency can be stabilized.

Asthma; IL9 as described in Shianan No. 58-136160
This also has the effect of eliminating the need for compensation for the 8 wave number changes of the 0° phase shifter.

4. Drawings? IJf simple one-shot h-! , Figure 1 is a 10 block diagram of a simple example of the present invention, and Figure 2 is a block diagram of another embodiment of the invention.

4...Second local vibration oscillator 7.8...Phase detector Vt device 15, 16, 19...Multiplier procedure amendment (spontaneous) Incident indication Patent application No. 208188 invention of 1982 Name Relationship to the case of person who corrects the demodulation circuit Patent applicant Name (5
101 Hitachi, Ltd. Style Person 1, “With” in line 10, page 3 of the specification, “through”
Correct.

2. Correct "phase shifter 10" on page 4, line 16 of the specification to "phase shifter 10."

& Add the following sentence between lines 9 and 10 on page 7 of the specification.

[Here, a detailed explanation will be given of the case where the present invention has a small intermediate frequency and feeds back to a local oscillator for tuning. FIG. 5 is the pull diagram.

101 is an adder, 102 is a tuning voltage generator that controls a local oscillator for tuning, and 103 is a switch.

104 is a control circuit, 105 is a control voltage input terminal, 106
is the control voltage output terminal.

At the time of channel selection, the control circuit 104 opens the switch 103, 'further changes the output voltage of the channel selection voltage generator 102, and controls the local oscillator 2 via the adder 101 to select the channel. Thereafter, by closing the switch 103 and adding the control voltage due to the phase error of the output of the loop filter 1B to the tuning voltage using the adder 101 to control the local oscillator 2, stable tuning and demodulation can be achieved.

"4. "This is a block diagram" in the first line of page 8 of the specification.
is corrected to "Block diagram. FIG. 3 is a block diagram of a part of still another embodiment of the present invention."

5. Add Figure 3 of the drawing as attached.

that's all Figure 3

Claims (1)

[Claims] 1. In a heterodyne receiver consisting of a mixer and a local oscillator, a reference oscillator corresponding to an intermediate frequency, 90°
A phase shifter, first and second phase detectors, and a loop filter are provided, and the reference oscillation leakage output is applied to the first phase detector and the second phase detector is applied via the 90° phase shifter. a demodulation circuit, further comprising applying the first and second phase detector outputs to the multiplier, and applying the multiplier output to the local oscillator via the loop filter. 2. In claim 1, first and second determination circuits, first and second multipliers, and subtracters are provided, and the outputs of the first and second phase detectors are used to convert the outputs of the first and second phase detectors to the first and second determination circuits, respectively. and a second judgment circuit, and also adds the first phase detector output and the second judgment circuit output to the first multiplier, and adds the second phase detector output and the first judgment circuit output to the first multiplier. adding the determination circuit output to the second multiplier, and subtracting the other multiplication value from the multiplication value of one of the first and second multipliers in the subtracter;
A demodulation circuit characterized in that the demodulation circuit is applied to the local oscillator via the loop filter.