JPS6149845B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a phase-shifting synergistic FM demodulator.

FIG. 1 is a circuit diagram showing the principle of a phase-shifting synergistic FM demodulator. In FIG. 1, 1 is an FM intermediate signal input terminal, and 2 is an amplifier that amplifies the intermediate frequency signal supplied to the input terminal 1. The amplifier has, for example, a limiter function that limits the amplitude of the intermediate frequency signal. A differential direct-coupled amplifier is used.
3 shows a phase-shift synergistic demodulator that demodulates the signal from the amplifier 2, and the demodulation circuit has a first differential pair of transistors 311 and 312 that switches based on the FM intermediate frequency signal _S2 from the amplifier 2. The FM signal is phase-shifted by a switching circuit 31 and a phase shift element 321 that shifts the phase of the FM intermediate frequency signal.
A phase shifter 32 is connected in series to the resonant circuit 322 that converts the phase of the intermediate frequency signal _S2 ' (frequency), and the differential transistor 311 of the first switching circuit 31, and the phase of the intermediate frequency signal S2' (frequency) is converted by the phase shifter 32. a second switching circuit 33 consisting of a differential pair of transistors 331 and 332 that switches based on the signal S ₂ '; a detection circuit 34 that detects the signal appearing at the output stage of the second switching circuit; and a demodulation circuit of a demodulation circuit. It includes an output resistor 35 and the like that determine the magnitude of the output. Most of the circuit 100 surrounded by dotted lines is integrated, and the resonant circuit 322 is provided with a resonant resistor 323, which is an external component to improve the distortion of the demodulated output. . Note that 4 and 5 are low-pass filters, and 6 is a tuning indicator.

In the demodulator shown in FIG. 1, the first switching circuit 31 is driven by the FM intermediate frequency signal S ₂ supplied to its input terminal, and the first switching circuit 31 is driven by the signal S ₂ ' phase-shifted by the phase shifter 32. 2 switching circuit 33, and diodes (or resistors) 361, 3 provided at the output stage of the second switching circuit 33.
Constant current source circuit 37 only during the period when there is an input signal in 62.
If the constant current I ₃₇ is conducted, the diode 361,
A current signal having a pulse width corresponding to the phase difference between the signals S ₂ and S ₂ ' flows through 362, and the voltage change signals of the diodes 361 and 362 generated by this signal are passed through the low-pass filter 4 and the average value thereof is taken out. , the DC voltage changes according to the above phase difference, so if the input signal is FM modulated,
FM demodulated. Note that the demodulation operation of the demodulator 3 will be described later. Since the theory is the same as that of the embodiment of the present invention, a detailed explanation thereof will be omitted here.

By the way, users of the new demodulator components may wish to change the magnitude of the demodulated output as necessary, for example, depending on the amplifier at the subsequent stage of the demodulator.

However, in the conventional circuit described above, it is difficult to realize this for the following reasons.

That is, in the conventional circuit shown in FIG. 1, there are two possible means for changing the magnitude of the demodulated output. One is to adjust the resonant resistor 323 of the resonant circuit 32, which is an external component, which affects the distortion of the demodulated output as well as the magnitude of the output, and the other is to integrate the output resistor 35 when manufacturing the demodulator 3. The output resistor is provided outside the circuit 100, that is, as an external component, and the resistance value of the output resistor is changed.

However, the former method has the disadvantage that the distortion of the demodulated output changes as the demodulated output changes. That is, resonance resistance 3
When the resistance value R ₃₂₃ of the resonant circuit 32 is increased, the slope of the characteristic curve 322a of the frequency vs. phase characteristic of the resonant circuit 32 increases as shown in FIG. Resonant resistance 323
When the resistance value R ₃₂₃ is decreased, the slope of the characteristic curve is decreased, the demodulated output is decreased, and its distortion is also decreased. These matters are generally known. Note that FIG. 4a shows the resonant frequency characteristic 32 of the resonant circuit 322.
2b is a characteristic diagram showing 2b. In this case, since the resonant resistance 323 is small, the signals at both ends of the resonant circuit 32,
That is, the second switching signal S ₂ ' becomes smaller and the second switching signal S 2 ' becomes smaller.
The switching operation of the switching circuit 33 tends to be incomplete.

Moreover, the latter is not practical because when the demodulator is integrated, the demodulated output varies due to variations in resistance within the integrated circuit. The reason will be explained below.

In general integrated circuits, the variation in the relative ratio of resistance can be suppressed to ±5%, but the absolute value of the resistance varies by ±30%. For example, integrated circuit 100
If each resistance varies +30% from the specified value and its value increases by 1.3 times, the constant current I ₃₇ flowing through the constant current source circuit 37 decreases by 1/1.3, and the current flowing through each circuit accordingly decreases by 1/1.3. The current flowing through the output resistor 35 also decreases. That is, when the circuit elements surrounded by dotted lines in FIG. 1 are integrated, the constant current source circuit 37
The resistance values of the resistors 315, 316, 373, etc. related to the setting of the constant current I ₃₇ vary from the specified value within the above range, and this causes the constant current I 37 to vary from the specified value.
I ₃₇ also varies. For example, if the above resistance varies by +30% and its value increases by 1.3 times, the constant current I ₃₇ will be 1/
It decreases to 1.3. Here, if the output resistance 35 varies by +30% like the above-mentioned resistance of the integrated circuit 100, and its value becomes 1.3 times, the voltage drop that occurs in the output resistance 35, that is, the output signal will not vary, but if the output resistance 35 is removed. Since it is an attached component, this output resistor 35 does not vary in the same way as the resistance in the integrated circuit 100, and moreover, it does not vary in the magnitude of the constant current I ₃₇ determined by the internal resistance of the integrated circuit 100 and the magnitude of the external output resistor 35. Since there is no correlation, a varying demodulated output will be obtained at the output terminal.

In view of the above-mentioned problems, an object of the present invention is to perform demodulation without adversely affecting the demodulated output and demodulation function (distortion, incomplete switching operation), suppress variations in the demodulated output, and reduce the magnitude of the demodulated output. The purpose is to provide a phase-shifting synergistic FM demodulator that can be changed accordingly.

In order to achieve the above object, the present invention configures a resonant resistor that affects the demodulated output in an integrated circuit together with a switching circuit and the like, and uses the output resistor as an external component.

According to the present invention, since the constant current of the constant current source circuit and the accompanying deviation in the demodulated output due to the deviation in the internal resistance of the integrated circuit are corrected by the resonant resistor, variations in the demodulated output can be suppressed and the stability is stabilized. It is possible to obtain a demodulated output.

Further, according to the present invention, since the output resistor is an external component, the magnitude of the demodulated output can be changed as appropriate by selecting the output resistor.

Embodiments of the present invention will be described below based on the drawings. FIG. 2 is a circuit diagram showing one embodiment of the present invention. In FIG. 2, the same parts as in FIG. 1 are designated by the same numbers.

In FIG. 2, reference numeral 300 denotes a gate circuit whose gate opens and closes in response to the output signal S ₂ from the amplifier 2; A second switching circuit 33 consisting of 332 is provided. The common emitter of the differential pair transistors 311 and 312 is the constant current source circuit 3.
It is connected to the ground terminal 11 through 7. The base of the transistor 311 is connected to the input terminal 1 through the amplifier 2, and is also connected to the ground terminal 11 through a resistor 315 and a bias power supply 317. The collector is a differential pair transistor 331,3
32 common emitters. The base of the transistor 312 is connected to the ground terminal 11 through a resistor 316 and a bias power supply 317, and the collector is connected to the power supply terminal 12 and the terminal 13 through a resistor 363. The base of the transistor 331 is a resistor 335 and a bias power supply 3.
It is connected to the ground terminal 11 through 37, and is also connected to the terminal 14. The base of the transistor 332 is connected to the ground terminal 11 through a resistor 336 and a bias power supply 337. The constant current source circuit 37 includes a transistor 371, a power source 372, and a resistor 373, and the constant current _I37 of the circuit is determined by the power source 372 and the resistor 373. resistance 31
5, 316, 335, 336, and 363 are bias resistances of the switching circuits 31 and 33. The resistance value of the resistor 335 is set to be as small as possible within a range that allows the switching circuit 33 to perform stable switching operations. In the embodiment, one resistor 335 serves as both the resonance resistor and the bias resistor, but it goes without saying that these resistors may be provided separately.

361 and 362 indicate diodes, and the cathodes of the diodes 361 and 362 are connected to the transistor 33, respectively.
1,332 collectors, and both anodes are connected to the power supply terminal 12. 34 indicates a subtraction circuit for detecting gate output signals appearing in the diodes 361 and 362 and subtracting those signals;
42, a transistor 343 and a diode 344 that absorb the current flowing through these transistors. The base of the transistor 341 is connected to the collector of the transistor 331 of the switching circuit 33, and the emitter is connected to the power supply terminal 12.
The collector is connected to the base of transistor 343. The base of the transistor 342 is connected to the collector of the transistor 332 of the switching circuit 33, the emitter is connected to the power supply terminal 12, and the collector is connected to the collector of the transistor 343. The base and emitter of the transistor 343 are connected directly to the ground terminal 11 through the diode 344, and the collector is connected to the output terminal 15. 32 is a phase shift collector 321 that shifts the phase of the FM intermediate frequency signal derived to the terminal 13, and a resonant circuit that converts the phase of the phase shift signal (frequency) shifted by the phase shift coil and guides it to the terminal 14. 322.
Resonant circuit 322 includes coil 3221 and capacitor 3
It consists of 222 parallel circuits, one end of which is connected to terminal 14.
The other end is connected to terminal 16 and capacitor 381.
It is grounded through. Here, the resonant circuit 32
As the second filter, a ceramic filter or the like may be used. In addition, the capacitor 381 is not an essential requirement to achieve the above purpose, and the capacitor 381 is not an essential requirement for achieving the above purpose.
This is necessary when the power source 7 is used as a reference power source for a tuning indicator 6, which will be described later. By grounding one end of the resonant circuit 322 in this way, the voltage of the bias power supply 337 is applied to the terminal 16 of the resistor 33.
5, terminal 14, and the resonant circuit 322, so this terminal 16 can be used as a reference voltage terminal. Therefore, as will be described later, when it is desired to visually adjust the demodulated output distortion using the tuning indicator 6, it is not necessary to provide a terminal for this purpose in the integrated circuit 100. One end of the phase shift coil 321 is connected to the terminal 14 through a capacitor 382, and the other end is connected to the terminal 13. Reference numeral 35 indicates an output resistor, which is connected between terminals 15 and 16. The output resistor 35 is an external resistor provided outside the integrated circuit 100. 4 indicates a low-pass filter provided at the next stage of the output resistor 35;
In other words, the FM intermediate frequency signal S ₂ applied to the first and second switching circuits, its phase-shifted signal S ₂ ', and the high frequency components generated by switching are removed and sent to the terminal 41. This is to extract the demodulated signal (audio signal). Reference numeral 5 designates a low-pass filter provided at the next stage of the filter 4 and having a time constant sufficiently larger than that of the filter 4, and this filter extracts the DC change signal appearing at the terminal 41, that is, the terminal 15. 6 is filter 5 and terminal 16
This shows a tuning indicator connected between terminals 15 and 16, which detects the voltage difference between terminals 15 and 16 and swings according to the detection level, and is used when setting the distortion of the demodulated output to the minimum. Ru. In this way, terminal 16
i.e., the bias power supply 337 of the integrated circuit 100
By using the voltage taken out through the terminal 14 and the phase shifter 32 as the reference voltage of the tuning indicator 6, the number of terminals (terminal 17 in Fig. 1) conventionally provided for taking out the bias power supply 337 is reduced. can. 7 indicates an ON-OFF switch of the automatic frequency control circuit (not shown), the fixed terminal OFF of this switch is connected to the terminal 16, and the fixed terminal ON is connected to the filter 5.
The movable terminal is connected to a local oscillator (not shown) through an automatic frequency control circuit.

Next, the demodulation operation will be explained.

In the circuit shown in FIG. 2, when there is no signal, each transistor of the first and second switching circuits 31, 33 is in an ON state, and the transistors 311, 33 are in an ON state.
A DC current with the same amplitude (1/2I ₃₇ ) flows through transistors 312 and diodes 361 and 362, respectively, and a DC current with the same amplitude (1/4
It is set so that a direct current of I ₃₇ ) flows through the transistors 341 and 342 of the subtraction circuit 34, and the same direct current as the current flowing through the diodes 361 and 362 flows through the transistors 341 and 342 of the subtraction circuit 34. That is, it is set so that the DC signal does not flow from the output terminal of the subtraction circuit 34 to the output resistor 35 side, or vice versa. Therefore, at this time, the output terminal 15 and the voltage reference terminal 16 are at the same potential, and no direct current flows through the output resistor 35 connected between these terminals. Further, the tuning indicator 6 does not swing.

Next, when an unmodulated FM intermediate frequency signal is supplied to the input terminal 1, the input signal is amplified and amplitude limited by the amplifier 2, and the output terminal of the amplifier has a rectangular waveform as shown in FIG. 3A. The output signal of S ₂
It is derived as This signal S ₂ is supplied to the bases of the differential pair transistors 311 of the first switching circuit 31 . Then, the transistor 311 turns on and off every 1/2 cycle of the signal S ₂ , and in response to this transistor, the transistor 312 also turns on the signal S ₂ .
It turns on and off every 1/2 cycle. That is, the transistors 311 and 312 alternately switch ON and OFF every 1/2 period of the signal _S2 . FIGS. 3B and 3C are waveform diagrams showing these switching operations. Further, the signal S ₂ is passed through the transistor 312 of the first switching circuit 31 to the phase shifter 32.
is supplied to the input terminal 13 of. Here, phase shift device 3
2 is designed so that when the signal S ₂ resonates at the resonance frequency ₀ of the resonant circuit 322, the phase of the signal is shifted by approximately π/2 (90°). In the following description, in order to simplify the explanation, the phase shift shift caused by the phase shift device 32 is assumed to be π/2 (90 degrees). When the signal S ₂ is detuned from the resonant frequency ₀ of the resonant circuit 322, a phase shift occurs based on the frequency versus phase characteristic curve 322a of the resonant circuit 322 shown in FIG. 4b.

Therefore, when the signal S ₂ resonates in the resonant circuit 32 and has a resonant frequency _{of 0} , the signal S ₂ supplied to the phase shifter 32 is phase-shifted by π/2 (90°) by the phase shifter, for example, the third As shown by the solid line waveform in Figure E, π/2 (90
゜) Lagging phase shift is derived to its output terminal 14. The delayed phase signal S ₂ ' derived from the terminal 14 is supplied to the bases of the differential pair transistors 331 of the second switching circuit 33. Then, the transistor 331 turns on and off every 1/2 period of the signal S ₂ ', and in response to this transistor, the transistor 332 also turns on and off.
Turns on and off every 1/2 period of S ₂ ′. That is, the transistors 331 and 332 alternately switch ON and OFF every 1/2 period of the signal S ₂ '.
FIGS. 3E and 3F are waveform diagrams showing these switching operations.

In such a switching operation, the transistor 311 of the first switching circuit 31 is turned on.
When the transistor 331 of the second switching circuit 33 is turned on, a current I ₃₆₁ flows through the diode 361 as shown in FIG. 3G, that is, in the 1/4 period region of the signal S ₂ . The current I ₃₆₁ at this time is It is.

Further, when the transistor 311 of the first switching circuit 31 is turned on and the transistor 332 of the second switching circuit 33 is turned on, the diode 36 is turned on.
2, a current I ₃₆₂ flows in the 1/4 period region of the signal S ₂ as shown in FIG. 3H. Current at this time I ₃₆₂
teeth It is.

These currents flow into the subtraction circuit 34, but since the currents I ₃₆₁ and I ₃₆₂ at this time match the currents flowing through the diodes 361 and 362 when there is no signal as described above, the output terminals of the subtraction circuit 34 As in the case of no signal, there is no potential current flowing in or out. Therefore, at this time as well, the output terminal 15 and the voltage reference terminal 16 maintain the same potential, and no current flows through the output resistor 35. Also, the tuning indicator 6 does not swing.

Next, a modulated FM intermediate frequency signal is supplied to the input terminal 1, and the frequency of the input signal is shifted by the frequency △ from the resonance frequency ₀ of the resonant circuit 322 due to the modulation, and its phase is shifted by the dotted line in FIG. 3E. When the phase is shifted by θ as shown in FIG. 3, the transistors 311 and 312 of the first switching circuit 31 perform a switching operation with a phase shift of o as shown by the dotted lines in FIG. 3E and F. Therefore the diodes 361, 36
The area of current flowing through the circuit 2 is as shown in FIGS. 3I and 3J. The currents I ₃₆₁ and I 362 flowing through the diodes 361 and ₃₆₂ at this time are becomes.

As can be seen from the above, the current flowing through the diode 361 increases by I ₃₇ o/2π due to the phase shift o, and the current flowing through the diode 362 decreases by I ₃₇ θ/2π due to the phase shift o. do.

That is, the average current flowing through the diodes 361 and 362 changes in proportion to the phase shift θ, that is, the frequency shift Δ from the resonance frequency ₀ of the resonant circuit 322, as seen from equations (3) and (4) above.

This changing current I ₃₇ θ/2π is supplied to the subtraction circuit 34, where I ₃₇ (1/4+o/2π)−I ₃₇ (1/4−θ/2π)
= I ₃₇ o/π is subtracted and guided to the output resistor 35, and the output current of I ₃₇ = I ₃₇ θ/π (5) flows through the output resistor 35, and the resistor has e=2I ₃₇ o/π・R ₃₅ …(6) θ=K△ …(7) However, the proportionality constant of K…△−△θ conversion e=I ₃₇・K/π・R ₃₅ △ …(8) The output signal is obtained. It will be done. Therefore, by supplying this output signal to the low-pass filter 4 and removing its harmonic components, a demodulated signal can be obtained at the output terminal 41.

As can be seen from equation (8) above, the magnitude of this demodulated signal is determined by the constant current I ₃₇ of the constant current source circuit 37, the resistance value R ₃₅ of the output resistor 35, and the slope of the frequency versus phase characteristic curve of the resonant circuit 322. determined by

Therefore, if you want to change the magnitude of the demodulated output, you only need to change one of these three, but in the circuit shown in FIG. Since the resonant resistor that affects the frequency vs. phase characteristics is integrated, it is not possible to freely set the magnitude of the demodulated output. In this case, there is no other option than the output resistor 35.

Hereinafter, it will be explained how variations in the demodulated output due to variations in the resistance of the integrated circuit 100 can be suppressed and how the magnitude of the demodulated output can be freely set.

In the circuit shown in FIG. 2, if, for example, the resistance 373 of the integrated circuit 100 varies by +30% and its value becomes 1.3 times as described in the conventional example, then the amount of constant current I ₃₇ of the constant current source circuit 37 is 1/ 1.3, and following this, the current flowing through the output resistor 35 also decreases, and the demodulated output generated in the output resistor tends to decrease accordingly. However, at this time, the resonant circuit 322
The value of the resonant resistance (bias resistance 355) is
Since it becomes 1.3 times larger, the slope of the frequency vs. phase characteristic curve 322a of the resonant circuit 322 shown in FIG. 4b increases, and the demodulated output increases.
This effect causes variations in the resistance of integrated circuit 100. This suppresses the decrease in demodulation output.

Frequency versus phase characteristic curve 322 of resonant circuit 322
As can _be seen from FIG.
is proportional to. Also, the resonant resistor 33 of the resonant circuit 322
By setting 5 sufficiently small compared to the resistance value of the tuning circuit itself, the frequency vs. phase characteristic curve 322a
The slope of can be made proportional to the resistance 335.

In this way, in FIG. 2, the resonant resistor 335 of the resonant circuit 322 is provided in the integrated circuit 100, and the resonant resistor corrects the deviation in the demodulated output due to the deviation in the absolute value of the internal resistance of the integrated circuit 100. , the demodulated output does not vary.

Further, since variations in the demodulated output due to the integration of the demodulator are corrected using the resonance resistor 335 of the resonance circuit 32, there is no need to integrate the output resistor 35, and it is possible to attach it externally. Therefore, by selecting this external output resistor 35, the demodulated output can be changed as appropriate.

Furthermore, since the resistor 335 is set to a small resistance value, the slope of the frequency versus phase characteristic curve of the resonant circuit 322 is small, and therefore the distortion of the demodulated output is small.

Further, when the reference voltage within the integrated circuit 100 is used as the reference voltage of the tuning indicator as in the above embodiment, the reference voltage within the integrated circuit 100, that is, the bias power supply 3
By conducting the voltage of 17 through the terminal 14 of the integrated circuit 100 and the resonant circuit 322, a dedicated terminal can be omitted, and the number of terminals of the integrated circuit 100 can be reduced by one. Therefore, it is suitable for integrated circuit formation.

In the demodulator described above, the change in DC voltage at the output terminal 15 when an output signal flows through the output resistor 35 is derived through the low-pass filters 4 and 5, and is added to one end of the tuning indicator 6. When the reference voltage of the reference voltage terminal 16 is applied to the other end, the indicator 6 swings according to the voltage difference between the two voltages. This shows that the input FM intermediate frequency signal is not tuned to the resonant circuit 322.

Furthermore, in the circuit shown in FIG. 2, the oscillation signal of the local oscillator (not shown) causes a drift due to environmental conditions, and the input signal to the FM intermediate signal input terminal 1 deviates from the tuning frequency ₀ of the resonant circuit 322. When the distortion of the demodulated output increases, the DC signal derived through the low-pass filter 5 is used as an automatic frequency control signal, and the automatic frequency control is turned on.
The distortion can be corrected by applying the signal to the local oscillator through an OFF switch and controlling the oscillation frequency of the local oscillator using the signal. The switch 7 is normally switched to the fixed terminal OFF, the reference voltage from the reference voltage terminal 16 is applied to the local oscillator, and the local oscillator is in a stable state.

[Brief explanation of the drawing]

FIG. 1 is a wiring diagram showing the principle of a phase-shifting synergistic FM demodulator, FIG. 2 is a wiring diagram showing a phase-shifting synergistic FM demodulator according to the present invention, and FIG. 3 is a waveform diagram for explaining the present invention. FIG. 4 is a frequency versus phase characteristic diagram of a resonant circuit used for explaining the present invention. DESCRIPTION OF SYMBOLS 1... Input terminal, 2... Amplifier, 31, 33... Switching circuit, 32... Phase shift device, 34... Subtraction circuit, 35... Output resistance, 37... Constant current source circuit, 4,
5... Filter, 6... Tuning indicator, 7... Automatic frequency control ON/OFF switch.

Claims (1)

[Claims] 1. Connected to the FM signal input terminal, and connected to the FM signal input terminal.
a first switching circuit including a first differential pair transistor that switches in response to an FM signal; and a second differential pair transistor including a second differential pair transistor coupled to one of the first differential pair transistors of the first switching circuit. a switching circuit; a constant current source that is coupled to the first differential pair transistor of the first switching circuit and includes a resistor that sets the constant current thereof; A resistor that sets the base bias of the transistor,
a bias circuit including a power supply; a bias circuit coupled to the other output terminal of the first differential pair transistor of the first switching circuit and one input terminal of the second differential pair transistor of the second switching circuit; The switching circuit includes a phase shift element that shifts the phase of the FM signal of the switching circuit, and a resonant circuit that resonates with the FM signal phase-shifted by the phase shift element and converts the phase of the frequency of the resonant FM signal. and a phase shifter that converts the phase of the frequency of the phase-shifted FM signal and guides it to the second switching circuit, and a resistor that is connected in parallel to the resonant circuit and acts as a resonant resistor having a demodulation output and distortion compensation function. and the second above
a detection circuit coupled to the output terminal of the second differential pair of transistors of the switching circuit to detect the output signal of the transistor; and an output coupled to the output terminal of the detection circuit to determine the magnitude of the output signal of the circuit. and a resistor having the function of the resonant resistor is integrated into an integrated circuit together with at least the first and second switching circuits, the constant power source, and the bias circuit, and is related to the constant current setting of the constant current source of the integrated circuit. However, the variation in the demodulated output due to the variation in each of the resistors is suppressed by the variation in the resonant resistor, the output resistor is an external component of the integrated circuit, and the demodulated output can be varied by the output resistor. Features: Phase shift synergistic FM demodulator. 2. The shifting synergistic FM demodulator according to claim 1, wherein the resonant resistance is set to a resistance value smaller than the resonant resistance value of the resonant circuit itself.