JPS58218246A - Mpx demodulator - Google Patents

Abstract

PURPOSE:To prevent deterioration in separation due to the phase characteristics of a BPF while reducing the influence of a disturbing signal by separating a left and a right channel signal from each other in front of the BPF and detecting a subsignal as an SSB wave. CONSTITUTION:A composite signal is applied to an LPF 11, delay circuit 14, and PLL 15 and the output of the LPF 11 is applied to one input terminal of a multiplier 12. The subcarrier signal of the PLL 15 is applied to the other terminal of the multiplier 12, whose output is applied though an amplifier 13 to an adding circuit 16 and a subtracting circuit 17. Further, the composite signal passed through the circuit 14 is applied to the circuits 16 and 17, whose outputs are sent to multiplying circuits 20 and 21 through BPFs 18 and 19. Further, the subcarrier signal is applied from the PLL 15 to those circuits 20 and 21, whose outputs are applied to LPFs 22 and 23, which output the left and right channel signals to reduce the influence of the disturbing signal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention detects only the lower sideband or upper sideband of a Sago signal, which is a DSB modulated wave, to remove interference signals in pilot tone FM stereo signal demodulation. MPX demodulator featuring two features! be.

Conventionally, in order to perform MPX demodulation by detecting only the lower sideband or upper sideband of a sub-signal, a configuration as shown in FIG. 1 has been used. The composite signal is filtered by bandpass filter 1. PLL circuit 4. The signal is input to an addition circuit 5 and a subtraction i-path 6. The output of the bandpass filter 4-1 is connected to one input of the multiplication circuit 2, and the 3 8 KHz subcarrier obtained by the PI, L circuit 4 is input to the other input. The output of the multiplier circuit 3 is connected to the amplifier 3.

Its output #i is connected to an addition circuit 5 and a subtraction circuit 6. The outputs of the addition circuit 5 and the subtraction circuit 6 are respectively connected to a low-pass filter 7.8, and their outputs become a right channel (Leh) output and a right channel (Rch) output.

A bandpass filter 1 extracts only the lower sideband or upper sideband of the sub-signal from the composite signal obtained by the FM detector. Take only the lower sideband]
In order to output the pass band 1d of the band pass filter 4-1
In order to extract only the upper sideband from 23 KHz to 38 KHz, the pass band is from 38 KHz to 53 KHs. The extracted single sideband is converted to P by the multiplication circuit 2.
It is multiplied by the 3 8 KHz subcarrier obtained by the LL circuit 4. This demodulates the sub-signal.

The output of multiplication circuit 2 is amplified to the same level as the main signal by amplifier 3, and then multiplied by addition circuit 5 and subtraction circuit 6.
+3 is given. This is similar to matrix 7 for conventional MPX demodulation.

The output of the addition circuit 5 is passed through a low-pass filter 7, where only low frequency signal components are extracted and become the Lcb output. The output of the subtraction circuit 6 passes through a low-pass filter 8 and becomes an RCh output. With this configuration, for example, the interference signal can be reduced to 38 KHz.
~53KI (z) If the lower sideband is detected, the demodulated signal will be less affected by interference.

Although the characteristics of the bass fill 4-1 are sharpened, the influence of interference waves is small, but the disturbance of the phase characteristics makes it impossible to obtain satisfactory separation characteristics. ,'1(
1 (i.) Therefore, this invention was made to solve the above-mentioned problems, and it is an object of the present invention to realize excellent separation characteristics that could not be obtained with the conventional configuration, and to have sufficient interference No. 1 removal performance. The aim is to provide a post-tuning circuit for the resulting MPX.

FIG. 2 shows the configuration of the present invention. The composite signal has low pass filters 4-11. Delay circuit 14, PLL circuit 15
added to. The output of the low-pass filter J-11 is input to one side of the multiplication circuit 12020. The other input of the multiplication circuit 12 is 3 8 obtained by the tiPLL circuit 15.
A KHz subcarrier signal is added. Multiplication circuit 12
The output of is connected to an amplifier 13, and its output is connected to an addition circuit 16 and a subtraction circuit 17 for falsification. The composite signal passed through the delay circuit 14 is applied to the other inputs of the addition circuit 16 and the subtraction circuit 17. Addition circuit 16
A band pass filter 18 is connected to the output of , and its output is connected to one side input of the multiplication circuit≠j,O. Multiplication circuit 20
38KH from tiPLL circuit 15 to one input of
The z subcarrier signal is added. A low-pass filter 22 is connected to the output of the multiplication circuit 2o.
Lch output is obtained. Similarly, a bandpass filter 4-19 is connected to the output of the subtraction circuit 17, and its output becomes one side input of the multiplication circuit 210. Also, the other input is the same as 20, 38KBz of t''-PLL circuit 15
Subcarrier is applied. The output of the multiplication circuit 21 is connected to a low-pass filter 23, and its output is Rc
h output.

Next, the operation will be explained. The reason for the lack of separation in the conventional configuration shown in Figure III is that only one sideband of the sub signal is extracted and detected using a bandpass filter, so the main signal (L + R) and the sub signal (
This is because the phase error between L and R is too large.

Normally, the interference signal exists on the upper sideband side, so the lower sideband is often detected. The phase characteristics of the band become extremely disordered. Therefore, when the main signal (L+R) and sub signal (L-R) are matrixed, crosstalk cannot be completely canceled. In the present invention, in order to eliminate the above-mentioned drawbacks, before passing through the bandpass filter 4-, the Lcht is converted into a sub-region signal containing only #1Rch, and even if the phase is disturbed by the bandpass filter, the separation will worsen. I'm making you look like Shinakomi. The beat generated by the multiplier is removed from the FM-detected composite signal by a low-pass filter 11, while the beat generated by the multiplier is removed by the low-pass filter 11.
A circuit 14 is provided to compensate for the delay time of this low-pass filter 11. The output of the low-pass filter 4-11 is multiplied by a 38 KHz subcarrier in a multiplication circuit 12. If the multiplication circuit 12 is a switching type such as a double-balanced differential, the low-pass filter 11 and delay circuit 14 are necessary, but if a linear multiplier circuit such as a Gilbert multiplier is used, the low-pass filter 11 is not necessary. . Multiplication circuit 12
The output is amplified by an amplifier 13 and added to the composite signal that has passed through the delay circuit 14 in an adder circuit 16. Further, in a subtraction circuit 17, the output signal is subtracted from the output of the output delay circuit 14 of the amplifier 13. The signal in the area around the 38 KHz subcarrier signal at the 0 point and the D point, which are the outputs of these 16° 17, becomes a signal containing only Lch information at the 0 point and only Lch information at the D point. Below, these are expressed mathematically as follows: Composite signal C(t) with the pilot signal at point B omitted:
t ・−−−−−・−−−−(suWst == 2
X The delay time is several MS and can be ignored for the most part.Also, when a linear multiplier circuit is used, a low-pass filter is not needed, so this delay time term is omitted in the calculation. Therefore, the output of the multiplier circuit 12 at point A is multiplied by the composite signal C(t)!=+carrier 5inWst, so cos2Wst...
- River...(2) As seen from the above equation, by multiplying by the subcarrier 5inWst, the original composite signal c(t)o main signal (L+R) becomes 38K
The signal is converted into the subcarrier signal region around Hz, and the subsignal (L-R) Fi, t-tio region and two of the subcarriers are
It has been converted to twice the frequency domain. Amplifier 1311 amplifies the composite signal multiplied by this subcarrier, serving as gain adjustment and buffer. When this amplified signal is added to the original composite signal and the output of the amplifier 13 in the adder circuit 16h, the output point C is as follows: -(L-R)+(L 'l)R)SinW
st-(LR)Cog2Wst.

1 1 2 ・・・・・・(2) Point B: (L+R) + (LR) 5inWat
・-= ...... River (1) 0 points: -! -(3L+R)+2 L Si nWs t--(L-R) C
o s 2SVs t-----I3) 2 Since the output point of the subtraction circuit 17 is point A - point B, ...................................... (4) (3 ) to the output point C of the addition circuit 16, which is 38K.
In the sub-signal region around the Hz subcarrier signal, only the uL multiplied signal exists, while from equation (4), only the R signal exists at the output point of the subtraction circuit 17, and these are double sideband (DSB) waves. It becomes.

The spectrum at point C on Si3 diagram is shown. The upper sideband (38
KH Atsushi~53KHz) or lower sideband (23KHz~3
After selecting and extracting one of the 8KH signals, the multiplication circuit 20 multiplies or switches the subcarrier signal 5inWst, and the low-pass filter 22 extracts the audio signal to obtain an Lch output. Furthermore, the output of the subtraction circuit 17 is also filtered through a bandpass filter 19.
After passing through, the signal is multiplied by the multiplication circuit 21 and the audio signal is extracted by the low-pass filter 23, and a Reh output is obtained in the same way as the sLch.

Here, if a linear multiplier is used in the multiplication circuit 12 as described above, the low pass filter 4-11 and the delay circuit 14 are unnecessary. Also, the delay circuit 14IIi can be omitted except when obtaining particularly high separation.For general interference signals such as nearby broadcasting stations, it is effective to use the lower sideband #1, but the band The pass filters 18 and 19 may be provided for both the upper side wave band and the lower 1111 wave band respectively) and may be switched by a switch.

In addition, the multiplication circuit 20.21 is used to detect the SSB wave (single sideband wave) extracted by bandpass, but in addition, after injecting the subcarrier B in Ws t, it is detected by a diode, so-called. Similar effects can be obtained with envelope detection, and it is not limited to SSB wave detection methods.

As described above, according to the present invention, since the pilot tone type sub-signal tDsB wave is detected as a<, SSB wave, the influence of interference is extremely reduced. Also, before passing through the band pass filter, the left and right
Since it is a sub-signal separated into R, separation is not deteriorated by the phase characteristics of the band-pass filter, and therefore the characteristics of the band-pass filter can be made sufficiently sharp.

[Brief explanation of drawings]

The m1 diagram is the conventional MPXull! Diagram showing Ill device, fl
Figure E2 is a diagram showing an example of the present invention, and Figure 3 is a diagram showing an example of the present invention.
FIG. 3 is a diagram showing a spectrum of points. 1.18.19... Bandpass filter 2.1
2, 20.21... Multiplication circuit 3.13...
...Amplifier ・:14.15...PLL 5.16...Addition circuit 2□'ζ,; 6.17...Subtraction circuit 11.7 , 8.22, 2.11...Low pass filter 14...--Delay circuit patent applicant

Claims (1)

[Claims] Convert the composite signal to a signal in the subcarrier signal region including left channel and right channel information using a subcarrier signal, extract the lower sideband or upper 9A wideband of each converted signal, and perform single sideband detection. The second feature is that the left channel and right channel signal outputs are obtained by
PX demodulator.