JPH10209904A - Receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure the stable calls with no increase of the cost by using a wide analog band filter which has its pass areas of all speech channels to perform the A/D conversion after the frequency conversion and to perform the narrow band filter processing via the digital complex signal processing. SOLUTION: The received signal undergoes the frequency conversion into an IF band signal which inputted to an input terminal 1 to undergo the band limitation via a wide band pass filter 9. Then the received signal is multiplied by the DC local oscillation signal produced by an oscillator 4 and a 90-degree phase shifter 5 via the multipliers 3i and 3q. The multiplied signal undergoes the DC detection at a base band, and the detection output is transmitted through the low band pass filters 6i and 6q for elimination of the higher harmonic components. Then the received signal is converted a digital signal by the A/D converters 7i and 7q. The digital signal undergoes the arithmetic processing via a complex processing circuit 10 and then undergoes the narrow band limitation via the digital low band pass filters 11i and 11q. Then the digital signal is demodulated by a demodulator 8 and outputted to an output terminal 15. Thus, no IF filter equalizer is required for correction of the characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver for demodulating a digitally modulated signal using a digital signal processing technique.

[0002]

2. Description of the Related Art An example of a conventional receiver will be described with reference to a block diagram of FIG. 1 is an input terminal, 2 is a band-pass filter, 3i is a multiplier of an in-phase component I of an IF band signal, and 3q is an IF
Multiplier for quadrature component Q of band signal, 4 for oscillator, 5 for 90 degree phase shifter, 6i for low-pass filter for in-phase component, 6q for low-pass filter for quadrature component, 7 for A / D converter, 8 is a demodulator,
15 is an output terminal. The received signal is frequency-converted into an IF band signal, input to an input terminal 1, band-limited by a band-pass filter 2, and a quadrature local oscillation signal generated by an oscillator 4 and a 90-degree phase shifter 5 is multiplied by a multiplier 3 i. Multiply by 3q,
Perform quadrature detection. The in-phase component I and the quadrature component Q of the quadrature detection output signal are passed through low-pass filters 6i and 6q to remove harmonic components, and then converted into digital signals by A / D converters 7i and 7q. After that, it is demodulated by demodulator 8 and output terminal 1
Output to 5.

[0003]

In the above-mentioned conventional example, a narrow-band analog filter is used as the band-pass filter. However, in recent years, the communication bandwidth tends to be narrowed with the increase in communication demand, and a bandpass filter is required to have a flat passband characteristic and a steep cutoff characteristic. It is technically difficult to realize the filter characteristics described above. Therefore, there is a problem that the manufacturing cost of the filter is increased, and an IF filter equalizer for correcting the characteristics is required, and the manufacturing cost is further increased. In addition, a large number of filters must be prepared to cover a wide communication channel, which causes a problem that the cost increases. Further, even if the center frequency of the filter slightly changes, it becomes difficult to talk, so that the requirement for the stability of the circuit becomes severe.

[0004] It is an object of the present invention to obviate these disadvantages,
It is to provide an inexpensive and highly accurate receiver.

[0005]

In order to achieve the above object, the present invention uses a wide-band analog band-pass filter having a pass band for all communication channels, and performs A-to-A conversion after frequency conversion.
The receiver is constructed by performing / D conversion and performing narrow band filter processing by digital complex signal processing.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. 1 is an input terminal, 9 is a broadband pass filter, 3i is a multiplier of the in-phase component I of the IF band signal, and 3q is an IF
A multiplier of the quadrature component I of the band signal, 4 is an oscillator, 5 is a 90-degree phase shifter, 6i is a low-pass filter of an in-phase component, 6q is a low-pass filter of a quadrature component, 7 is an A / D converter, 10 is a complex processing circuit, 11i is a digital low-pass filter of an in-phase component, 11q is a digital low-pass filter of a quadrature component, 12
Is an integrator, 13 is a read-only memory (ROM), 8 is a demodulator, and 15 is an output terminal. The received signal is frequency-converted into an IF band signal and then input to the input terminal 1, band-limited by the broadband pass filter 9, and a quadrature local oscillation signal generated by the oscillator 4 and the 90-degree phase shifter 5 is multiplied by the multiplier 3 i Multiply the received signal by 3q and perform quadrature detection in the baseband. The quadrature detection output is passed through low-pass filters 6i and 6q to remove harmonic components, then converted into digital signals by A / D converters 7i and 7q, and subjected to complex arithmetic processing by a complex processing circuit 10 to obtain a digital low-pass signal. Narrow band limitation is performed by the bandpass filters 11i and 11q. Then demodulated by demodulator 8,
Output to the output terminal 15. Here, since the oscillator 4 is not synchronized with the demodulator 8 and uses the wide band pass filter 9, a frequency shift occurs as shown in FIG. 4, for example.
Therefore, the output of the demodulator 8 is stored in the ROM 13 through the integrator 12 and fed back to the complex processing circuit 10 to stop the rotation of the phase and obtain a complex processing output by quasi-synchronous detection that adjusts the center frequency. . FIG. 3 shows an example of the internal configuration of the complex processing circuit 10. As shown in FIG. The complex processing circuit 10 includes multipliers 16i-1, 16i-2, 16q-1, 16q-2 and adders 17i, 17q.
The operation is as shown in equation (1). I ′ = I cosωt-Q sinωt Q ′ = Q cosωt + I sinωt Equation (1) where I ′ is the complex processing circuit output of the in-phase component, Q ′ is the complex processing circuit output of the quadrature component, and I is the Complex processing circuit input, Q is the complex processing circuit input of the orthogonal component. When the oscillator 4 of FIG. 1 is configured as a voltage-controlled oscillator as an application example of the present invention, synchronization can be achieved by feeding back the output of the demodulator 8 to the oscillator 4, and the complex processing circuit 10 is omitted. be able to. With the above operation, a high-accuracy receiver output can be obtained by a combination of a wideband analog filter and a narrowband filter processing by digital processing. The above embodiment is applied to a direct detection system, and is suitable for detecting an AM modulated wave.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 5 is an example in which the present invention is applied to a heterodyne detection system, where 1 is an input terminal, 9 is a broadband pass filter,
3i is a multiplier of the in-phase component I of the IF band signal, 3q is a multiplier of the quadrature component I of the IF band signal, 4 is an oscillator, 5 is a 90-degree phase shifter, 6i is a low-pass filter of the in-phase component, 6q is A quadrature component low-pass filter, 7i and 7q are A / D converters, 14 is a complex digital filter, 8 is a demodulator, and 15 is an output terminal. The received signal is frequency-converted into an IF band signal, input to the input terminal 1, and band-limited by the wide band pass filter 9.
The received signals are multiplied by the quadrature local oscillation signals generated by the oscillator 4 and the 90-degree phase shifter 5 by the multipliers 3i and 3q, and quadrature detection is performed in the baseband. The quadrature detection output is subjected to low-pass filters 6i and 6q to remove harmonic components, and then converted to digital signals by A / D converters 7i and 7q.
Filter processing is performed by the complex digital filter 14.
An example of the configuration of the complex digital filter 14 is shown in FIG. 1
7i-26i and 17q-26q are multipliers, 27i-29i and 27q
29q to 30q are adders, and 30i to 33i and 30q to 33q are delay registers. When the filter processing is expressed by an equation, the following equation (2) is obtained. Y _I = H _R IH _I QY _Q = H _R Q + H _I I ... Equation (2) where Y _I , Y _Q : digital complex filter output, H _I , H _R : filter coefficients, I, Q: filter This is the input signal. The operation of the complex digital filter 14 of FIG.
This will be described with reference to the spectrum diagrams of FIGS. 8, 9, and 10. Fig. 7
Is the signal before complex filtering, that is, the A / D converter 7
Outputs I and Q of i and 7q. Where frequency fc and frequency
Although a signal appears at -fc, only one signal is required (here, the component of + fc) and the component of -fc is an image interference signal. In order to remove this image disturbance, a complex coefficient filter having a pass band only in a positive frequency band as shown in FIG. 9 is required. This complex coefficient filter is obtained by frequency-shifting the frequency characteristic of a real coefficient filter as shown in FIG. 8 by + fc. The filter of FIG. 8 is expressed by the following expression (3). H ₀ (Z) = a ₀ + a ₁ Z ^-1 + a ₂ Z ^-2 + ... + anZ ^-n (a ₀ to an): Filter coefficient ... Equation (3) where Z = e ^{j2πf / fs} (Fs: sampling frequency). Assuming that the center frequency of the filter is fc ′, fc ′ is fc
, The frequency f based on fc ′ is shifted to (f−fc). Therefore, Z = e ^{j2π (f-fc) / fs} = e ^{j2πf / fs}・ e ^{-j2πfc / fs} = Z ・ e ^{-j2πfc / fs} = Z ・ α (fs: sampling frequency)… Equation (4) where α = e ^{-j2πfc / fs} is a complex number whose absolute value is 1. Substituting equation (4) into equation (3) and rearranging, H ₀ (Z) = a ₀ + a ₁ α ^-1 Z ^-1 + a ₂ α ^-2 Z ^-2 + ... + anα ^-n Z ^-n = H _R0 + jH _I0 + (H _R1 + jH _I1 ) Z ^-1 + (H _R2 + jH _I2 ) Z ^-2 + ... + (H _R n + jH _I n) Z ^-n ... 5) and a complex coefficient filter is obtained. FIG. 6 shows a configuration of the complex coefficient filter. FIG. 9 shows the frequency characteristics of the frequency-shifted complex digital filter. Since this is a complex filter, the pass band is only one of the positive and negative frequencies (the positive frequency side in FIG. 9). FIG.
Is an output of the complex digital filter, and the image interference component is removed by the complex filter. Since the analog filter has a wide band, an image interference component overlaps with the IF signal, but the complex digital filter processing removes the image interference component and enables narrow-band filtering. This embodiment is suitable for detecting an FM modulated wave.

As described above, it is easy to realize a narrow band filter using a digital filter if the sampling frequency after frequency conversion is not so high. Further, after designing once, adjustment work such as an analog circuit is unnecessary, and the cost is hardly required.

[0009]

According to the present invention, a receiver capable of greatly reducing costs can be realized by performing narrow-band digital filter processing after A / D conversion using a wide-band analog filter.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional technique.

FIG. 3 is an internal structural diagram showing one embodiment of a complex processing circuit;

FIG. 4 is a spectrum diagram showing an embodiment of a baseband signal due to a shift of a center frequency.

FIG. 5 is a block diagram showing one embodiment of the present invention.

FIG. 6 is a block diagram showing an embodiment of the internal structure of a complex digital filter.

FIG. 7 is a spectrum diagram showing an example of an output signal from an A / D converter.

FIG. 8 is a spectrum diagram showing an example of a frequency characteristic (baseband) of a complex digital filter.

FIG. 9 is a spectrum diagram showing an example of the frequency characteristic of the complex digital filter after the frequency shift.

FIG. 10 is a spectrum diagram showing an example of an output signal of a complex digital filter.

[Explanation of symbols]

1: input terminal, 2: band-pass filter, 3i, 3q: multiplier, 4: oscillator, 5: 90-degree phase shifter, 6i, 6q: low-pass filter, 7i, 7q: A / D converter, 8 : Demodulator, 9: wide band pass filter, 10: complex processing circuit, 11i, 11q: digital low pass filter, 1
2: integrator, 13: ROM, 14: complex digital filter, 15: receiver output, 16i-1, 16i-2, 16q-1,
16q-2: Multiplier, 17i-26i, 17q-26q: Multiplier, 27i-29i, 27q-29q: Adder, 30i-33
i, 30q to 33q: delay register.

Claims (4)

[Claims] 1. A reception signal is passed through an analog wide band pass filter in which all communication channels are in a pass band, multiplied by orthogonal local signals, and frequency-converted into orthogonal intermediate frequency signals.
A receiver characterized in that after performing A / D conversion, digital narrow band filtering is performed to obtain a demodulated output. 2. The receiver according to claim 1, wherein the A / D
A receiver which performs complex arithmetic processing after the conversion to correct a frequency shift generated when the frequency is converted to the orthogonal intermediate frequency signal. 3. The receiver according to claim 1, wherein a signal subjected to frequency conversion to an intermediate frequency is filtered by a complex digital filter to remove an image interference component and obtain a demodulated output. 4. An input terminal for inputting a reception signal which is frequency-converted into an IF band signal, an analog wideband filter having a pass band for all communication channels of the reception signal input to the input terminal, and a signal after passing through the filter. Oscillator and 90-degree phase shifter for quadrature detection of in-phase and quadrature components 2
Two multipliers, an in-phase component for removing harmonic components of the in-phase component and the quadrature component signal detected by the multiplier,
A low-pass filter for each of the orthogonal components, and an A /
A D converter, a complex processing circuit for performing complex processing on the in-phase and quadrature digital signals from the A / D converter, and selecting digital signals of the in-phase and quadrature components processed by the complex circuit for each single communication channel An in-phase and quadrature narrow-band digital low-pass filter, a demodulator for demodulating and outputting a band-limited signal output from both filters, an integrator for integrating the output of the demodulator, A ROM for reading phase information data corresponding to the output of the integrator and outputting the read data to the complex processing circuit, wherein the position of the complex processing circuit is corrected based on the phase information data. Machine.