JPS6022686Y2 - FM stereo demodulator device - Google Patents

Description

[Detailed description of the invention] This invention is particularly suitable for integrating FM receivers into integrated circuits.
The present invention relates to a stereo demodulator device.

Conventionally, in FM receivers, so-called PLL-MP
A stereo demodulator called X-IC and designed to be an integrated circuit is used.

However, in this PLL-MPX-IC (multiplex integrated circuit using a phase-locked loop),
Since at least 14 pins are required, the package housing this IC must be a so-called dual in-line package, and a single in-line package (9 pins or less), which is advantageous for mounting, cannot be used.

This is the low pass filter (LPF) used in such ICs.
This is because it is difficult to reduce the number of pins because it is a two-terminal type.

That is, one low-pass filter is used for phase synchronization and one for stereo detection, which inevitably increases the number of required terminals.

For this reason, there is an idea to use a terminal-type low-pass filter, but in that case, the contacts of the low-pass filter would be outside the IC, and noise would enter between it and the ground point inside the IC, making it impractical. Ta.

In this case, the main noise component is the potential difference caused by the connection resistance between the terminal and the internal ground point because a large current of several IQmA for the stereo indicator lamp flows during stereo.

Therefore, this idea was made in view of the above points, and it is an object of the present invention to provide an improved FM stereo demodulator device that eliminates noise intrusion caused by integrated circuits and reduces the number of pins as much as possible. It is intended to.

An embodiment of this invention will be described in detail below with reference to the drawings.

That is, as shown in FIG.
first and second phase comparator circuits 1 connected via
3.14 as well as a switching demodulator circuit 12, a second pin 9 connected to the output end of the first phase comparator circuit 13, and an input end connected to the output end of the first phase comparator circuit 13. A connected voltage controlled oscillator circuit (VCO) 16 with a free running frequency of 76 kHz, and this voltage controlled oscillator circuit 16
the third pin 8 connected to the oscillation frequency determining section of the voltage controlled oscillator circuit 16; A master flip-flop circuit 19 has an input terminal connected to it and an output terminal connected to the other input terminal of the first phase comparator circuit 13, and an input terminal is connected to the output terminal of this master flip-flop circuit 19. a slave flip-flop circuit 21 whose output end is connected to the other input end of the second phase comparator circuit 14; and a fourth pin 7 connected to the output end of the second phase comparator circuit 14. , a Schmitt circuit 23 whose input end is connected to the output end of the second phase comparator circuit 14, and a control input end connected to the first output end of this Schmitt circuit 23, whose input end is
a stereo switch circuit 20 connected to the output end of the frequency divider circuit 18 and whose output end is connected to the other input end of the switching demodulator circuit 12; and a control input connected to the second output end of the Schmitt circuit 23. a connected lamp drive circuit 24, fifth and sixth pins 5 and 4 connected to the first power terminal and second power terminal of the lamp drive circuit 24 in correspondence with each other, and the switching demodulator circuit 1.
2 and the seventh and eighth pins 2 and 3 respectively connected to the first and second output ends of the circuits 11 to
13゜16.18~21, 23.24 other circuits excluding lamp drive circuit 24 11~13, 16゜18~
an integrated circuit 10 for an FM stereo demodulator comprising a ninth pin 6 commonly connected to the power supply terminal of 21.23;
Pin 9. 7. The first and second low-pass filters 15 each have one terminal type and are connected correspondingly to the filters 8.
．． 22, an integrating circuit 17, and a lamp 25, one end of which is connected to the fifth pin 5 outside the integrated circuit 10, and a first voltage Vcc is connected to the ninth pin 6. A first power supply VCC is commonly connected to each reference potential point of the first and second low-pass filters 15.17 and the integrating circuit 22, and a second power supply VL is connected to the other end of the lamp 25. 6 is grounded, and an FM stereo composite signal is input from the outside to the first pin 1, and outputs separated into left and right channels are derived from the seventh and eighth pins 2 and 3 to the outside. This is an FM stereo demodulator device characterized in that it is configured such that the lamp 25 can be turned on and the lamp 25 can be turned on.

Therefore, in the above configuration, the FM supplied to pin 1
The stereo composite input signal is fed via a buffer (amplifier) circuit 11 to a switching demodulator circuit 12 and to a first and second phase comparator circuit 13.14.
supplied to

Here, the first phase comparator circuit 13 is a one-terminal type first low-pass filter (LP) connected to the outside via pin 9.
F) 15, a voltage controlled oscillator circuit (VCO) 16 with a free-running frequency of 76 kHz (an integration circuit 17 for determining the oscillation frequency is externally connected to this VCO via pin 8), and a 172 frequency divider circuit. 18 and a master flip-flop circuit 19 constitute a phase locked loop (PLL).

In other words, 76 kHz from the VCO 16 is converted to 38 kHz by the 172 frequency divider circuit 17 and supplied to the stereo switch circuit 20 (described later), and further converted to 19 kHz (phase 90°) by the master flip-flop circuit 19 for the first phase comparison. drive circuit 13.

Then, a loop works to synchronize the phase of this 19kHz to the pilot signal in the FM stereo composite signal, and the VCO 16 is controlled by the DC component of the phase difference signal taken out via the first LPF l5. .

On the other hand, 19kHz from the slave flip-flop circuit 21 connected to the master flip-flop circuit 19
2 (phase 0°) drives the second phase comparator circuit 14.

In other words, the PLL locks to the 19kHz pilot signal in the FM stereo composite signal, and its output goes to pin 7.
A one-terminal second low-pass filter (LP
F) When the voltage reaches a predetermined level or higher via 22, the Schmitt circuit 23 is activated.

As a result, the stereo switch circuit 20 described above is opened, and the lamp drive circuit 24 is driven so that a current (V
The lamp 25 connected to the outside via a lamp power supply (■) separate from the lamp cc) lights up to indicate that the FM stereo signal is being received.

Furthermore, the aforementioned switching demodulator 12 to which 38 kHz is supplied via the stereo switch circuit 20 switches the FM stereo composite signal using the 38 kHz signal as a switching signal, so that the output pins 2 and 3 are separated into left and right channels. produces an output.

By the way, pin 6 has a common power supply (Vcc) for each circuit in the above integrated circuit (excluding the lamp drive circuit).
is connected to this power supply (Vcc), and the first and second LPFs 15 and 22, each of one terminal type, are connected to this power supply (Vcc).
The connection of each end of the integrator circuit 17 provides one feature of the present invention that prevents noise from entering the integrated circuit.

In other words, unlike the lamp power supply (Vt) through which a large current flows as mentioned above, this means that the power supply (Vcc) side, where the current does not fluctuate much and is less prone to noise components, is used as the reference potential for each low-pass filter and integration circuit. This is because it is possible to prevent the intrusion of noise components as in the conventional case due to the influence of the lamp current.

Moreover, since the low-pass filter is of one-terminal type according to such a connection, the number of pins can be reduced accordingly.

In other words, an integrated circuit for an FM stereo demodulator having the same functions as a conventional PLL-■)X-IC can be contained within 9 pins in total, so it can be accommodated in a single in-line package, which is advantageous for implementation as an integrated circuit. and can be extremely useful.

FIG. 2 shows a specific example of the first and second phase comparator circuits described above, and includes a double bounce stage amplifier (DBA) consisting of transistors Q1 to Q9 and a direct current lamp (DCA).
It consists of

In other words, the stereo composite signal e2 is supplied to the lower input base of the double balance amplifier (DBA), and this is supplied to the input base of the double balance stage at 19kHz (
A phase comparison output is obtained by switching with a switching signal e1 (normally a square wave), and this phase comparison output is converted to DC by a capacitor C that serves as a low-pass filter and extracted, and then amplified to a predetermined level by a DC amplifier (DCA). This is what I did.

It goes without saying that various modifications can be made without departing from the gist of the invention.

Therefore, as detailed above, this invention provides an extremely good FM stereo demodulator device that is improved so as to eliminate noise intrusion caused by integrated circuits and to reduce the number of pins as much as possible. becomes possible.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of essential parts showing an embodiment of an FM stereo demodulator device according to the invention, and FIG. 2 is a circuit connection diagram showing a specific example of the phase comparator circuit of FIG. 1. ■・・・Integrated circuit, 11・・・Buffer (
amplifier) circuit, 12... Switching demodulator circuit, 13.14... Phase comparator circuit, 15.2
2...Low pass filter, 16...Voltage controlled oscillator circuit (VCO), 17...Integrator circuit, 18...1/2 frequency divider circuit, 19,21・
... Flip-flop circuit, 20 ... Stereo switch circuit, 23 ... Schmitt circuit, 24 ... Lamp drive circuit, 25 ...
...Lamp, 1 to 9...Zen, vCC...
・Power supply, vL... Lamp power supply.

Claims (1)

[Scope of utility model registration request] a first pin, first and second phase comparator circuits and a switching demodulator circuit each having one input end connected to the first pin via a buffer circuit; a second pin connected to the output end, a voltage controlled oscillator circuit whose input end is connected to the output end of the first phase comparator circuit and has a free running frequency of 76 kHz, and an oscillation frequency determining section of the voltage controlled oscillator circuit. a 1/2 frequency divider circuit connected to the output terminal of the voltage controlled oscillator circuit; an input terminal is connected to the output terminal of the 172 frequency divider circuit; a master flip-flop circuit connected to the other input end of the first phase comparator circuit; an input end connected to the output end of the master flip-flop circuit; and an output end connected to the input end of the second phase comparator circuit; a slave flip-flop circuit connected to the other end, a fourth pin connected to the output end of the second phase comparator circuit, and an input end connected to the output end of the second phase comparator circuit. a Schmitt circuit, a control input terminal connected to a first output terminal of the Schmitt circuit, an input terminal connected to an output terminal of the 172 frequency divider circuit, and an output terminal connected to the other input terminal of the switching demodulator circuit. a lamp drive circuit having a control input terminal connected to the second output terminal of the Schmitt circuit; and a lamp drive circuit having a control input terminal connected to the second output terminal of the Schmitt circuit; 5 and 6 pins, seventh and eighth pins respectively connected to the first and second output terminals of the switching demodulator circuit, and other circuits other than the lamp drive circuit among the respective circuits. a ninth pin commonly connected to the power supply terminal of the FM stereo demodulator integrated circuit; The lamp includes first and second low-pass filters and an integrating circuit each having one terminal type, and a lamp having one end connected to the fifth pin outside the integrated circuit, and a lamp having a first end connected to the ninth pin. A power supply is connected, and the first power supply is commonly connected to each reference potential point of the first and second low-pass filters and the integrating circuit, and a second power supply is connected to the other end of the lamp, and the sixth with the seventh and eighth pins grounded and an FM stereo composite signal input from the outside to the first pin.
An FM stereo demodulator device characterized in that the output separated into the left channel can be led out from the pin of the FM stereo demodulator device, and the lamp can be lit.