JPH03201607A - Fm demodulator - Google Patents

Abstract

PURPOSE:To make a signal processing easy and to improve the stability of the signal processing by converting an inputted FM modulated wave signal to a base band signal, afterwards, digitizing the signal and executing the signal processing of demodulation. CONSTITUTION:An orthogonal detecting means 10 is provided to execute the orthogonal detection of the inputted FM modulated wave signal and to lead out plural base band signals, and an A/D conversion circuit 12 is provided to lead out plural amplitude information signals while being supplied with the plural base band signals. Further, an orthogonal phase converting means 14 is provided to lead out a phase information signal while being supplied with the plural amplitude information signals, and a phase difference detecting means 16 is provided to lead out a phase difference signal from the phase information signal. Then, a D/A conversion circuit 18 is provided to lead out an analog demodulation signal while being supplied with the phase difference signal. Thus, since the demodulation processing is executed from the digital signal of a base band, a digital signal processing is easily executed by forming an IC, etc., and device scale is reduced. Further, the stability of the signal processing is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to FMt! :Regarding modulators, in particular, it relates to an FM demodulator that performs digital signal processing after deriving a baseband signal from an FM modulated wave, thereby reducing the device scale and providing excellent signal processing stability.

[Prior Art] Conventionally, this type of FM demodulator has been known as a Foster Schiele type discriminator circuit, a double-tuned discriminator circuit, a ratio detection circuit, a delayed linear quadrature detection circuit, a pulse count type, etc. The suitable circuit is selected and used.

These circuits are supplied with an intermediate frequency signal (IF multiplied signal) obtained by frequency-converting the received signal transmitted by wire or wirelessly. Then, a demodulated signal related to desired audio, image, etc. information is derived. Ru.

3. Detailed Description of the Invention [Problem to be Solved by the Invention] However, in the FM demodulator according to the above-mentioned conventional technology, since information is demodulated from the FM signal having a relatively high frequency, high-speed operation is required, and its signal processing is relatively difficult. Furthermore, when an inductive M-coupling circuit (staggered tuning circuit, etc.) is provided, such as a Foster Schiele type discrimination circuit, double-tuned discrimination circuit, ratio detection circuit, etc., desired frequency band characteristics, especially characteristics in frequency bands near both ends, can be obtained. Causes deterioration. Furthermore, the tuning frequency fluctuates over a long period of time, and it is relatively difficult to maintain the tuning frequency. In this case, there are drawbacks such as the need for relatively laborious readjustment of the staggered tuning frequency.

The present invention has been made in view of the above-mentioned points.
It is an object of the present invention to provide an FM demodulator that facilitates digital signal processing such as digital signal processing, reduces the scale of the device, and has excellent signal processing stability.

[Means for Solving the Problems] In order to solve the above problems, the FM demodulator of the present invention includes orthogonal detection means for manually inputting an FM modulated wave signal and performing orthogonal detection to derive a complex baseband signal. , an A/D conversion circuit that is supplied with the complex baseband signal and derives a complex amplitude information signal; an orthogonal phase conversion circuit that is supplied with the complex amplitude information signal and derives a phase information signal; The present invention is characterized by comprising: a phase difference detection means that derives a phase difference signal from an information signal; and a D/A conversion circuit that is supplied with the phase difference signal and derives an analog demodulated signal.

[Operation] In the above configuration, the input FM modulated wave signal is converted into a baseband signal, and then digitized and demodulated signal processing is performed. After this, a demodulated signal related to modulation information of the analog signal is derived. In this case, signal processing is easy and stability of signal processing is improved.

[Embodiment] Next, an embodiment of the FM demodulator according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an example of the overall configuration of the embodiment, FIG. 2 is a block diagram showing a detailed configuration example of a quadrature detection circuit, and FIG.
The figure is a block diagram showing a detailed configuration example of an A/D conversion circuit,
FIG. 4 is a block diagram showing a detailed example of the configuration of the phase detection circuit, and FIG. 5 is a block diagram showing a detailed example of the configuration of the D/A conversion circuit.

First, the general structure and operation will be explained with reference to FIG. 1, and then the detailed structure and operation will be explained with reference to FIGS. 2 to 5.

In FIG. 1, reference numeral A is an FM demodulator, and the FM modulated wave signal Sa (hereinafter referred to as IF band as necessary) is an IF multiplied signal supplied from a frequency converter, etc. (not shown).
A quadrature detection circuit 10 that performs quadrature detection and derives real and imaginary (complex) baseband (BB) signals 3c and 3d, respectively, and instantaneous real and imaginary (complex) amplitude information. An A/D conversion circuit 12 that derives a signal 5eSSf is provided. Furthermore, a quadrature phase conversion circuit 14 that derives a phase information signal sh, a phase difference detection circuit 16 that derives a phase difference signal Sj, and a circuit D that derives an analog demodulated signal Sl.
/A conversion circuit 18 is provided.

Furthermore, the operation in this configuration will be explained.

The input FM modulated wave signal Sa is supplied to the quadrature detection circuit 10 and subjected to quadrature detection. Here, the real part and imaginary part B
It is converted into a B signal 55Sd. Then, BB signal 5cS
Sd is sampled and A/D converted by the A/D conversion circuit 12 and converted into instantaneous complex amplitude information signals Se, Sf (real part, imaginary part).Furthermore, the amplitude information signals Se, Sf are in quadrature phase. It is converted into a phase information signal sh in a conversion circuit 14. Then, it is converted into a phase difference signal Sj, which is the difference from the phase of one sample before, in a phase difference detection circuit 16. Then, D/
A demodulation signal Sl of the analog signal is generated in the A conversion circuit 18, and a modulation (information) signal related to the S part of the FM modulation wave signal is derived.

Next, the above configuration and operation will be explained in detail.

An example of the configuration of the quadrature detection circuit 10 is shown in FIG.

In this example, the multiplier 22 receives the FM modulated wave signal S part.
a, 22b, a local oscillator 24 that sends out a local oscillation frequency signal that is the same as the IF band, and a local oscillator 24 that sends out a local oscillation frequency signal that is the same as the IF band.
A phase shifter 26 is provided which shifts the phase by degrees.

Here, the input FM modulation wave signal S part is branched into two parts and input to multipliers 22a and 22b, respectively. The local oscillation frequency signal is then multiplied by the input multiplier 22a to generate a BB signal Sc in the BB band and the IF band (the real part of the S part of the FM modulated wave signal).Then, the phase shifter 26 - The local oscillation frequency signal phase-shifted by 90 degrees is input to the multiplier 22b, and is converted into a BB signal Sd with an imaginary part twice that of the BB band and the IF band.

An example of the configuration of the A/D conversion circuit 12 is shown in FIG.

This example uses low pass filters (LPF) 30a, 30b.
, A/D converters 32a and 32b, and a clock oscillator 34.

The real part BB signal Sc and the imaginary part BB signal Sd are each passed through an LPF.
30a and 30b remove frequency components twice the IF band, and A/D converters 32a and 32b perform A/D conversion with frequency limited to prevent aliasing noise. Then, the instantaneous real part and imaginary part amplitude information signals Se, S
f is derived. Note that the A/D sampling clock is supplied from the clock oscillator 34, and its frequency is set to more than twice the sum of the maximum frequency deviation of the FM modulated wave and the highest modulation frequency.

Next, the quadrature phase conversion circuit 14 converts the amplitude information signals Se, Sf
Read out the phase information using the amplitude value of as an address signal.
For example, a ROM (not shown) is used.

Here, a phase information signal sh is derived by converting the amplitude information of the amplitude information signals Se and Sf into phase information.

An example of the configuration of the phase difference detection circuit 16 is shown in FIG.

This example includes a subtracter 40 and a delay device 42.

The phase information signal sh is branched into two and sent to a subtracter 40 and a delay device 4.
2 is input. A phase difference signal Sj indicating the phase l samples before output from the delay device 42 and the phase difference thereof is output.

An example of the configuration of the D/A conversion circuit 18 is shown in FIG.

This example includes a D/A converter 50 and an LPF 52.

The input phase difference signal sj is converted into an analog amplitude signal according to the magnitude of the phase difference by the D/A converter 50, and then
The LPF 52 removes harmonics and derives a demodulated signal Sl.

In this way, the baseband band BB signals Sc, Sd
is digitized and subjected to signal processing, and then the demodulated signal S
I am getting f. Therefore, signal processing is easy and stability of signal processing can be obtained.

In the above embodiment, a separate circuit is configured for signal processing after the A/D conversion circuit 12, but the present invention is not limited to this. Microprocessor (M
Similar signal processing is performed using D/PU), etc., and then D/
Obtaining the demodulated signal Sl from the A conversion circuit 18 is also included in the present invention.

[Effects of the Invention] As described above, the FM demodulator of the present invention includes orthogonal detection means for receiving an FM modulated wave signal and performing orthogonal detection to derive a complex baseband signal; An A/D conversion circuit is supplied with a band signal and derives a complex amplitude information signal; an orthogonal phase conversion circuit is supplied with a complex amplitude information signal and derives a phase information signal; It is characterized by comprising a phase difference detection means for deriving the phase difference signal, and a D/A conversion circuit supplied with the phase difference signal and deriving the analog demodulated signal.

As a result, demodulation processing is performed from the baseband digital signal, facilitating digital signal processing using an IC or the like, reducing the scale of the device, and providing excellent stability of signal processing.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the FMl modulator according to the present invention; FIG. 2 is a block diagram showing the detailed configuration of the quadrature detection circuit shown in the embodiment of FIG. 1; 3 is a block diagram showing the detailed configuration of the A/D conversion circuit shown in the embodiment of FIG. 1, and FIG. 4 is a block diagram showing the detailed structure of the phase detection circuit shown in the embodiment of FIG. 1. , FIG. 5 is a block diagram showing the detailed configuration of the D/A conversion circuit shown in the embodiment of FIG. 1. 0... Quadrature detection circuit 2... A/D conversion circuit 4... Quadrature phase conversion circuit 6... Phase difference detection circuit 8... D/A conversion circuit 2a, 22b... Multiplier 4 ...Local oscillator Oa, 30b...Low pass filter (LPF) 2a,
32 b-A/D converter 4...Clock oscillator 0...Subtractor 2...Delay unit 0...D/A converter 2...LPF a...FM modulated wave signal cSSd. ...Baseband (BB) signal eSSf...
・Amplitude information signal h...Phase information signal S''...Phase difference signal SR...Demodulated signal

Claims (1)

[Claims] (1) Quadrature detection means to which an FM modulated wave signal is input and which performs orthogonal detection to derive a complex baseband signal; and an A/D converter to which the complex baseband signal is supplied and which derives a complex amplitude information signal. a circuit, quadrature phase conversion means to which the complex amplitude information signal is supplied and derive a phase information signal, phase difference detection means to derive a phase difference signal from the phase information signal, and a circuit to which the phase difference signal is supplied. An FM demodulator comprising: a D/A conversion circuit that derives an analog demodulated signal;