JPS61139105A - Am-fm demodulating circuit - Google Patents

Abstract

PURPOSE:To make a device low-cost and small-sized by providing a programmable divider which divides the frequency of the output of a voltage controlled oscillator and using the output of this divider for demodulation and taking out a modulated signal from a reception signal directly to make a front end for frequency conversion to an intermediate frequency unnecessary. CONSTITUTION:A circuit includes a wide band amplifier 2, a limiter 3, a phase comparator 4, a low-pass filter 5, a DC amplifier 6, a voltage controlled oscillator 9 using a varactor diode 15, a programmable divider 8, a pi/2 phase shifter 10, a mixer 11, and filters 12 and 19 which receive the output of this mixer. The output signal of the DC amplifier 6 is applied to one end of the varactor diode 15, and a tuning voltage is impressed to the other terminal, and the tuning voltage and the division value of the programmable divider 8 are controlled. Thus, the output frequency of the programmable divider 8 is changed in a wide range, and a PLL loop is locked if the output frequency of the programmable divider 8 is set to a desired reception signal frequency, and an AM or FM modulated signal is taken out directly from the reception signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an AM-FM demodulator, and particularly to an AM-FM demodulator intended for direct demodulation of AM/FM radio and television signals.

[Conventional technology]

Conventionally, FMa regulators include a phase comparator, a low-pass filter,
P consists of a DC amplifier and a voltage controlled oscillator (VCO).
There is an LL type demodulator. In addition, a PLL type demodulator is used as the AM demodulator, and the oscillation frequency of the VCO is fixed in P and LL. There is one system that allows you to extract the AM demodulated baseband signal by advancing the phase, making it in phase with the input signal, mixing the respective signals, and passing them through a low-pass filter.

[Problem that the invention seeks to solve]

Based on the fcgg mentioned above (AM will also soon be the v of the FM demodulation circuit
The CO converts the received signal, which has a small frequency variable range, into an intermediate frequency and then demodulates it, and therefore requires a front end for converting it into an intermediate frequency.

Therefore, there is a drawback that the cost of the equipment is high or the area occupied is increased.

[Elaborate means to solve problems]

The AM-FM demodulator of the present invention receives the output of a wideband amplifier, a phase comparator, a low-pass filter, a DC amplifier, a ratio voltage controlled oscillator using a variable capacitance diode, a PLL circuit that creates a loop with a programmable divider, and a programmable divider. It has a 1c/2 phase shifter, a mixer that mixes the output of the π/2 phase shifter and the output of the wideband amplifier, and a filter that receives the output of this mixer.
The output of the C amplifier is used as the t-FM demodulation output, and the output of the low-pass filter after the mixer is 1Fr:O is used as the AM demodulation output to obtain an AM/FM demodulator that can demodulate either AM or FM input signals.

〔Example〕 The present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention, and T
The purpose is direct demodulation of V-band. First, a TV signal is inputted from a signal input terminal 1 and amplified by a wideband amplifier 2 . After the amplification by the broadband amplifier 2, the signal is branched on one side to a limiter 3 and on the other hand to a mixer 11. This [The video signal of the TV signal is AM modulated, so the input signal to the mixer 11 [IJ Mitter 3
This is because the AM component will be removed if the input signal is passed through the input limiter 3 to the phase comparator 4, and unless the levels are made the same, the synchronization holding range of the PLL will vary depending on the input level.

The phase comparator 4 outputs a phase error voltage between the output signal of the programmable divider 8 and the input signal, which is passed through the low-pass filter 5 and converted into a DC voltage. Further DC
The ratio signal amplified by the amplifier 6 is applied to the anode side of the variable capacitance diode 15, which changes the oscillation frequency of the vCO9.

The rooting output signal of vCO9 is divided into 1/N by programmable divider 8 and inputted to phase comparator 4, thereby forming a PLL loop.

The cathode side terminal 17 of the variable capacitance diode 15 is vC
This is a terminal to which an external tuning voltage is applied to forcefully vary the oscillation frequency of O9. If an appropriate voltage is applied to the tuning voltage terminal 17 to change the oscillation frequency of the vCO 9, the output frequency of the programmable divider 8 will change.

- 10,000, the frequency of the ratio signal input from the signal input terminal 1 and the output frequency of the programmable divider 8 become close to each other, and the PLL
If the input signal frequency is within the pull-in range of PLL, the input signal frequency and the output frequency of the programmable divider 8 will be equal.
The loop responds and fixes the oscillation frequency of vCO9. In this case, the output signal of the programmable divider 8 has the input signal = π/2 delay order phase relationship, the PLL loop is in a locked state, and the AM component is removed by the PLL loop.Only the tth carrier wave is removed. The signal is in a regenerated state.

Make this carrier in phase with the phase of the input signal, i.e. π
/2 Capacitor 10t-through mixer 1 to advance
Enter 1. The other side of the mixer 11 is connected to &AM11, which amplifies the signal input from the signal input terminal 1.

Now, the AM signal wave input to the mixer 11 is sent to the ACO 5 (
ωi + θ) and reproduced t carrier wave signal t-Bcqs(a
+t+θ), and if multiplied by mixer 11, Ac
os2θ) + co 5(0)) is outputted and passed through the low-pass filter 12, so that the term 2ωt+20 is not outputted. The cosQ wave is modulated by the amplitude of A previously defined as VCA COS (ωt+θ), which means that only the modulated signal can be extracted.

In reality, there are more signals input from the input terminal 1, and the signal is not multiplied by the 7't2 signal, but all other signals have a frequency 9 phase difference from the reproduced carrier wave. The sum and difference frequency components of the input frequency and the reproduced carrier frequency are output as outputs, and when the signal is passed through the low-pass filter 12, the sum and difference frequency components are removed.

The output signal of the mixer 11 contains video and audio subcarriers.Then, the signals are separated by a low-pass filter 12 and a band-pass filter 19. The subcarriers of each voice are output.

TV signal frequencies range widely from VHF to UHF, and in the American band, signals at approximately 50 MHz to 900 MHz't are input from the input terminal 1.

In this case, the oscillation frequency of VCO9 is set to an external source.

900MHz when controlled by the voltage applied to the gummy pressure terminal
It has a variable width twice that of ~18GHz (UHF
If you want to receive the band, programmable divider 80
If the division ratio is set to 1/2, the programmable divider 8
The output frequency is 450~900MHz, and if you set the programmable divider to gold 1/4, it will be 225~450MHz.
1115~225MH when H2% l/8! , 1
/ 16 f'156.25 ~ 1115MHz,
It is possible to demodulate all TV bands by arbitrarily controlling the oscillation frequency of VCOS and the division value of 10-gram pull divider 8. Direct demodulation is possible.

Here, the oscillation frequency t-2 times the VCO 9 is selected as the division value t-2, 4, 8°16 of the programmable divider 8.
．． This is because if a binary number such as 32, .

In addition, the signal output terminal 7 is provided at the output of the DC amplifier 6, because if the signal input to the input terminal 1 is FM, the FM demodulated output can be obtained by extracting the signal from the output terminal 7. This is because if this circuit is constructed from a semiconductor integrated circuit and an output terminal 7' is provided, both AM and FM signals can be demodulated with the same circuit.

〔Effect of the invention〕

That's all for explanation 7? ,In practice, the present invention provides a wideband amplifier, a limiter-1 phase comparator, a low-pass filter, an amplifier,
It consists of a voltage controlled oscillator using a variable capacitance diode, a programmable divider, a π/2 phase shifter, and a mixer, and the output signal of the DC amplifier is applied to one end of the variable capacitance diode, and the chaining voltage is applied to the other terminal. The chaining voltage and the division value of the programmable divider are controlled, and the output frequency of the programmable divider can be changed over a very wide range.If the output frequency of the programmable divider is set to the desired receiving signal frequency, the P
LL loop is locked, AM or FM from received signal
The modulated signal of t can be extracted across the t-direction. For this reason,
There is no need for a front end to convert the frequency to an intermediate frequency, and since most circuits are made of semiconductors, integration is easy, reducing equipment costs and reducing equipment costs.
This has the effect of making it smaller.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention. 1...Signal input terminal, 2...Broadband amplifier, 3...Limiter-14...Phase comparator, 5...Low pass filter , 6...
...DC amplifier, 7...FM demodulation output terminal,
8...Programmable divider, 9...
・Voltage controlled oscillator (VCO), 10...πl phase advance capacitor, 11...Mixer, 12...
...Low pass filter, 13 ... DC cut capacitor, 14 ... Tuning inductor, 15 ... Variable capacitance diode, 16 ...
... Bino (scan capacitor, 17... Chaining voltage terminal, 18... Video J video demodulation output terminal (AM demodulation output terminal), 19... Band pass filter, 20 ...Audio subcarrier demodulation output terminal (AM demodulation output terminal).

Claims (1)

[Claims] a wideband amplifier that receives an input signal, a phase comparator that receives the output of the wideband amplifier, a low-pass filter that receives the output of the phase comparator, a DC amplifier that amplifies the output of the low-pass filter, and a DC amplifier that amplifies the output of the DC amplifier. a voltage controlled oscillator using a variable capacitance diode whose capacitance is adjusted by the output of the DC amplifier;
a programmable divider for dividing the output of the voltage controlled oscillator; means for applying the output of the programmable divider to the phase comparator; a phase shifter for shifting the phase of the output of the programmable divider by 90°; An AM/FM demodulation circuit comprising: a mixer that mixes the output of the broadband amplifier; a filter that receives the output of the mixer; and a second output terminal that takes out the output of the filter.