JPH02111128A - Pilot signal eliminating circuit in stereo demodulator - Google Patents

Abstract

PURPOSE:To cancel a pilot signal and to improve S/N by generating a simulated sine wave signal at a simulated sine wave signal generating circuit based on a triangle wave signal from a triangle wave signal generating circuit and adding the simulated sine wave signal to a composite signal at a cancellation circuit. CONSTITUTION:A rectangular wave signal shaped by a waveform shaping circuit 4a is fed to a triangle wave generating circuit 4b. When transistors(TRs) Q4, Q5 in the triangle wave generating circuit 4b are turned on/off alternately by rectangular wave signals of opposite phase fed to the bases, a capacitor C applies charging/discharging and a triangle wave signal of opposite phase is obtained at each terminal of the capacitor. A simulated sine wave signal generating circuit 4d obtains a simulated sine wave signal by dulling a peak of a triangle wave signal inputted through the use of nonlinearity of the input output characteristic of a differential amplifier and supplies the result to the cancel circuit. As a result, the pilot signal in the composite signal is almost completely cancelled by the simulated sine wave signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pilot signal removal circuit in a stereo demodulator.

[Prior Art] In an FM receiver, a so-called MPX (multiplex) demodulator is used to independently separate left and right channel signals from an FM-detected composite signal. The MPX demodulator derives a 19K) & pilot signal from the composite signal to obtain a 38KHz subcarrier signal, and uses this subcarrier signal as a switch ink signal to separate left and right channel signals from the composite signal.

Since the composite signal includes a piezoelectric signal, it is inevitable that the pilot signal will also be switched and mixed into the left and right channel signals in a switched ink separation circuit using a subcarrier signal.

When the pilot signal is mixed into the channel signal in this way, the S/N ratio of the demodulated stereo signal decreases, so the MPX
Various pilot signal removal circuits have been proposed for actively canceling the 19 KHz pilot signal at the input stage of the demodulator.

As an example, 19 to 7 pilot signals are selectively detected from the composite signal, and the 38K signal is in phase with this signal.
PLL used to obtain Hz subcarrier signal
The 19 KHz rectangular wave signal from the (phase-locked loop) circuit is waveform-shaped to form a pilot cancellation signal consisting of a triangular wave, and this pilot cancellation signal is added to the composite signal at the input stage of the switch ink separation circuit to generate the pilot signal. A method of removal was used.

(Problems to be Solved by the Invention) The conventional pilot signal cancellation method described above has a relatively simple circuit configuration, but since the pilot cancellation signal is a triangular wave, it is difficult to completely remove the pilot signal consisting of a sine wave. However, there was a problem in that a 19 KHz component appeared in the output stage.

FIG. 4 shows a conventional removal method, and as is clear from the figure, the pilot signal Sp is removed by adding a pilot signal Sp made of a sine wave and a pilot cancellation signal Sk made of a triangular wave having the opposite phase. In this case, it is difficult to say that the S/N ratio of the stereo demodulated signal has been sufficiently improved because a non-removed component Se occurs and the pilot signal cannot be completely removed.

Therefore, the present invention provides a pilot signal removal aperture in a stereo demodulator that enables more complete removal of the pilot signal included in a composite signal. is the issue. It is characterized by converting it into a similar sine wave signal.

[Means to solve the problem]

In order to solve the above problems, the pilot signal removal circuit in the stereo demodulator according to the present invention is designed to switch in the FM-detected composite signal.
A rectangular wave signal circuit that generates a subcarrier signal for separating into two signals and a rectangular wave signal having the same frequency as the pilot signal, and a triangular wave signal based on the rectangular wave signal generated by the rectangular wave signal generating circuit. a triangular wave signal generating circuit that generates a triangular wave signal, and a pseudo sine wave signal generating circuit that generates a pseudo sine wave signal based on the triangular wave signal that the triangular wave signal generating circuit generates.
The present invention is characterized by comprising a wave signal generation circuit, and a cancellation circuit that adds the pseudo sine wave signal generated by the pseudo sine wave signal generation circuit and the composite signal to cancel the pilot signal in the composite signal.

Further, the pseudo sine wave signal generation circuit may
] In the above configuration, the pseudo sine wave signal generation circuit generates a pseudo sine wave signal based on the triangular wave signal from the triangular wave signal generation circuit, and this pseudo sine wave signal is added to the composite signal in the cancellation circuit. The pilot signal consisting of a sine wave in the composite signal is almost completely canceled.

[Example] Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram showing an embodiment of a pilot signal removal circuit in a stereo demodulator according to the present invention. In the figure, 1 is a cancellation circuit for canceling a pilot signal, and this circuit 1 uses a cancellation signal to remove a 19 KHz pilot signal from an FM-detected composite signal applied to an input terminal IN. 2 is MP
It is an X circuit, and demodulated outputs of R and L signals are obtained from the composite signal sent from the cancellation circuit 1 using the sub-rear signal. 3 is a PLL circuit that generates subcarriers, and is synchronized with the pilot signal of the composite signal applied to the input terminal IN, and is at a predetermined level.
8KHz and 19K) L! Detects the signal of 38KI (
The subcarrier signal of z is sent to the MPX circuit 2. Reference numeral 4 denotes a cancel signal generating circuit that generates a cancel signal, which generates a cancel signal consisting of a pseudo sine wave based on a 19 KHz rectangular wave signal from the PLL circuit 3.

FIG. 2 is a circuit diagram showing a specific circuit example of the cancel signal generating circuit 4, and in the same figure, the transistor Q
, and Q2 constitute a differential amplifier together with a constant current source consisting of a transistor Q, and the differential amplifier includes transistors Q,
and 19KHz from PLL circuit 3 added to Q2 (
The waveform shaping circuit 4a functions as a waveform shaping circuit 4a that shapes a rectangular wave signal (with a phase delay of 90° relative to a pilot signal) to align the peak-to-peak values of the rectangular wave. The rectangular wave signal whose waveform has been shaped by the waveform shaping circuit 4a is output between the collectors of the transistors Q and Q2.

The rectangular wave signal whose waveform has been shaped by the waveform shaping circuit 4a is applied to the triangular wave generating circuit 4b. Triangular wave generation circuit 4
b indicates transistors Q4 and Q that operate differentially, and a transistor Q that constitutes a constant current source for each of these transistors Q4 and Q5.

and Q7, and a capacitor C connected between the emitters of transistors Q4 and Q5. When transistors Q4 and Q are alternately turned on and off by opposite phase square wave signals applied to their bases, capacitor C charges and discharges, and a triangular wave signal of opposite phase is obtained at each terminal of the capacitor C. This differentially operated triangular wave generation circuit 4
With b, a triangular wave signal of a predetermined amplitude can be obtained with a capacitor half the capacitance of a capacitor that does not operate differentially, and the subsequent circuit can have a differential configuration.

The triangular wave signal outputted from the triangular wave generating circuit 4b to both terminals of the capacitor C is transmitted through the Darlington-connected transistors Q8 and Q, and the transistor Q1.
o and Q, and a transistor Q that operates as a constant current source.
+z and Q+3 are supplied to a pseudo sine wave signal generation circuit 4d via an impedance conversion/level shift/buffer amplifier 4c.

The pseudo sine wave signal generation circuit 4d consists of transistors Q + 4 and Q Is that constitute a differential amplifier, and transistors Q Ib and Q tw that constitute a constant current source. A pseudo sine wave signal is obtained by making use of the nonlinearity of the output characteristic to blunt the peak portion of the input triangular wave signal.

Note that the transistors Q + a and Q I of the differential amplifier
The variable resistor VR connected between the bases of It can be adjusted as desired. Further, E is a bias voltage source of the constant current source.

〔effect〕

As explained above, according to the present invention, the pilot signal in the composite signal is almost completely canceled by the pseudo sine wave signal generated based on the triangular wave signal, and the effect is that stereo demodulation with an excellent S/N ratio can be performed. is obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the general configuration of a pilot signal removal circuit in an FM demodulator according to the present invention, FIG. 2 is a circuit diagram showing a specific circuit configuration of a part of FIG. A characteristic diagram showing the characteristics of a part of the circuit in the figure, and FIG. 4 is an explanatory diagram for explaining the problems of the conventional method. ■...Cancel circuit, 2...MPX circuit, 3...
- PLL circuit, 4... Cancellation signal generation circuit, b... Triangular wave signal generation circuit, 4d... Pseudo sin wave signal generation circuit.

Claims (2)

[Claims] (1) A rectangular wave signal generation circuit that generates a subcarrier signal for separating an FM-detected composite signal into two signals by switching the composite signal, and also generates a rectangular wave signal having the same frequency as the pilot signal; A triangular wave signal generation circuit that generates a triangular wave signal based on a rectangular wave signal generated by the wave signal generation circuit; and a pseudo sine wave signal generation circuit that generates a pseudo sine wave signal based on the triangular wave signal generated by the triangular wave signal generation circuit. A pilot signal in a stereo demodulator, comprising: a canceling circuit that adds the pseudo sine wave signal generated by the pseudo sine wave signal generating circuit and the composite signal to cancel the pilot signal in the composite signal. removal circuit. (2) The pseudo sine wave signal generating circuit generates a triangular wave signal into a pseudo sine wave signal using the input/output saturation characteristics of the differential amplifier.
A pilot signal removal circuit in a stereo demodulator, characterized in that the circuit converts the pilot signal into a wave signal.