JP2002043850A - Wide-band digital receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that conventionally an IF frequency cannot be increased very high, since error noise is produced by the aperture jitter characteristics of a sampling signal supplied to an A/D converter in A/D conversion, and the valid number of bits (ENOB) is deteriorated, when a high-frequency reception signal is converted to an IF signal and is further converted into a digital signal by the A/D converter. SOLUTION: IF signal, digitized by a first A/D converter 8, is converted into analog by the D/A converter. The A/D and D/A converters 8 and 9 are operated by the sampling signal generated by the same signal generator 10, thus inhibiting the generation of error noise in conversion by aperture jitter. The output of the D/A converter 9 is subjected to bandwidth lamination by a required frequency by a filter 11 for converting into the digital signal by a second A/D converter 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver used in mobile communication, and more particularly, to a receiver for channel separation and demodulation.
The present invention relates to a compact and low-cost wideband digital receiver that does not deteriorate in performance when realized by a digital circuit such as an SP (Digital Signal Processor).

[0002]

2. Description of the Related Art In recent years, with the development of digital circuit technology, examples of realizing functions conventionally realized by analog circuits by digital circuits are increasing. When the function is implemented by a digital circuit, there are advantages that there is no variation in characteristics, there is no deterioration over time, and no adjustment is required. In addition, when a programmable device such as a DSP is used as the digital circuit, the function is described by software. Therefore, there is an advantage that correction and change are easy. In the field of mobile communications such as digital mobile phones, the transition to digital circuits is progressing. As an ultimate example, software radios (Joe Mitola, “The Software Radio Archi
tecture ”, IEEE Communication Magazine May 1995 Vo
1.33 No.5) has been proposed.

FIG. 3 is a schematic diagram showing an example of a conventional wideband digital receiver. A broadband digital receiver is a receiver that performs A / D conversion of a wideband signal as it is in an RF band or an IF band and performs signal processing after channel separation by a digital circuit. (Related patent: “Digital radio frequency receiver” Japanese Patent Application No. 61-504791) As shown in FIG.
RF bandpass filter 22, low noise amplifier 23, first
Mixer 24, first local oscillator 25, first IF bandpass filter 26, first IF signal amplifier 27, second mixer 28, second local oscillator 29, second IF bandpass filter 30, second IF signal amplifier 31, A / D conversion Unit 32, sampling signal generator 33 and DSP (Digital
SignalProcessor) 34.

In FIG. 3, a high-frequency reception signal received by an antenna 21 is input to an RF band-pass filter 22 and subjected to necessary band limitation. Here, the necessary band is a bandwidth receivable by the wideband digital receiver, and coincides with a service band band of a generally used system. The reception signal subjected to the band limitation by the RF bandpass filter 22 is amplified by the low noise amplifier 23,
The frequency is converted by the first mixer 24 and the first local oscillator 25, and a band is limited by the first IF band-pass filter 26 for removing an image to be a first IF signal.

The first IF signal is amplified by a first IF signal amplifier 27, frequency-converted by a second mixer 28 and a second local oscillator 29, and a second IF bandpass filter 30 restricts the band for image removal. The second IF signal has a frequency that allows the A / D converter 32 to operate. The second IF bandpass filter 30
Has the function of an anti-aliasing filter for A / D conversion in the A / D converter 32. The second IF signal is amplified by a second IF signal amplifier 31 and then A / D
The converter 32 converts the signal into a digital IF signal. At this time, a sampling signal is supplied from the sampling signal generator 33 to the A / D converter 32. This digital IF signal is subjected to channel separation and demodulation processing by the DSP 34 to become a demodulated signal.

[0006]

However, in the wideband digital receiver, error noise is generated at the time of A / D conversion due to the aperture jitter characteristic of the sampling signal supplied from the sampling signal generator to the A / D converter. As a result, the effective number of bits (ENOB) of the A / D converter deteriorates as described later.
This deterioration becomes more remarkable as the input frequency to the A / D converter increases. Therefore, the frequency of the input signal to the A / D converter, that is, the IF frequency cannot be made too high. Therefore, when the frequency of the high-frequency reception signal is high, it is necessary to take measures such as making the high-frequency reception circuit a double-conversion configuration and lowering the frequency. However, there is a drawback that the practicability of the method is reduced. Further, there are problems that the characteristics of the wideband digital receiver, such as no variation in characteristics, no deterioration over time, and no need for adjustment are not obtained.

FIG. 4 shows an example of characteristics of the input frequency versus ENOB in the case of a 12-bit A / D converter. In the figure, σa indicates the standard deviation σa of the aperture jitter of the sampling signal, and σa is several tens ps (picosecond: 10 ⁻¹² seconds) in a normal crystal oscillator. In the figure, σa is 10
When the input frequency exceeds 10 MHz, ENO
B greatly deteriorates due to the influence of the aperture jitter, and becomes about 8 bits at an input frequency of 60 MHz. In order to reduce such deterioration, it is necessary to reduce the input signal to several MHz or less. As a result, it is necessary to reduce the frequency of the input signal of the A / D converter by forming the high-frequency receiving circuit in a double conversion configuration. It becomes. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object to provide a wideband digital receiver having a high-frequency receiving circuit having a simple configuration without causing performance degradation.

[0008]

In order to achieve the above object, in a wideband digital receiver according to the present invention, a first A / D converter for converting an analog intermediate frequency signal into a digital signal; A D / A converter for converting an A / D converter output into an analog signal, a filter for band limiting the output frequency of the D / A converter, and a second for converting the band limited signal to a digital signal An A / D converter is provided, and the first A / D converter and the D / A converter are operated by a sampling signal generated by the same signal generator, so that the sampling signal is converted by aperture jitter. It is characterized in that the occurrence of error noise is suppressed, the frequency conversion is performed, and the A / D conversion is performed by the second A / D converter at a relatively low frequency.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in the drawings. FIG. 1 is a schematic configuration diagram showing one embodiment of a wideband digital receiver according to the present invention. As shown in FIG.
1, RF bandpass filter 2, low noise amplifier 3, mixer 4, local oscillator 5, IF bandpass filter 6,
IF signal amplifier 7, A / D converter 8, D / A converter 9,
Sampling signal generator 10, low-pass filter 11,
A / D converter 12, sampling signal generator 13 and D
SP14.

In FIG. 1, a received signal received by an antenna 1 is input to an RF bandpass filter 2 and subjected to necessary band limitation. Here, the necessary band is a bandwidth receivable by the wideband digital receiver, and coincides with a service band band of a generally used system.
Next, the R band-limited by the RF band-pass filter 2
The F reception signal is amplified by the low noise amplifier 3, frequency-converted by the mixer 4 and the local oscillator 5, band-limited for image removal by the IF band-pass filter 6, and becomes an IF signal. The IF band pass filter 6 has a function of an anti-aliasing filter for A / D conversion in the A / D converter 8.

The IF signal is amplified by an IF signal amplifier 7 and then converted into a digital IF signal by an A / D converter 8. This digital IF signal is converted by a D / A converter 9 into an analog IF signal. At this time, the converter 8
And the D / A converter 9 have the same sampling signal generator 10
Supplies a sampling signal. For this reason,,
The influence of the aperture jitter characteristic of the sampling signal is canceled. The converted analog IF signal is composed of an image signal and a signal that is down-converted to an area equal to or less than half the number of sampling frequencies as described later. Becomes the down-converted output signal.

FIG. 2 is a diagram for explaining the principle of frequency conversion according to the present invention. An input signal A / D converted at the sampling frequency fs by the A / D converter is converted into a D / A signal at the same sampling frequency fs. 4 shows a spectrum arrangement of an output signal after the / A conversion. When the input signal of the frequency fin is subjected to A / D conversion at the sampling frequency fs and further D / A converted, an image signal appears in the output signal every fs / 2 as shown in FIG. D
Since the fundamental frequency of the output signal of the / A converter appears at fout in the figure, the same spectrum as the input signal is obtained by cutting the high-order image signal with a low-pass filter.
ut. That is, the frequency conversion from fin to fout has been performed.

The image signal has two cases depending on the relationship between the sampling frequency fs and the input signal frequency fin. The frequency relationship in the case of FIG. 7A is expressed by Expression (1), and the frequency relationship in the case of FIG. 8B is expressed by Expression (2). fout = fin−k × fs (1) where k × fs <fin <(k + 1 /) × fsk = 0, 1, 2,... fout = (k + 1) fs−fs (2) where (k + 1) / 2) × fs <fin <(k + 1) × fs k = 0, 1, 2,... In the case of Expression (2), an inverted image is used. If the inconvenience such that demodulation cannot be performed properly with this operation occurs, the spectrum may be inverted again.

The analog IF signal output from the D / A converter 9 passes through a low-pass filter 11 for extracting the lowest signal of the image signals shown in FIG. 2, and is converted into a digital signal by an A / D converter 12. Is converted. This A /
The sampling signal is supplied from the sampling signal generator 13 to the D converter 12, but since the input signal frequency (frequency of the analog IF signal) is low, the influence of aperture jitter is small. This digital signal is subjected to channel separation and demodulation processing in the DSP 14 and output as a demodulated signal.

[0015]

As described above, according to the present invention,
Since the IF frequency for performing A / D conversion can be set higher than that of the conventional method, a broadband digital receiver having an RF front-end circuit having a simple configuration can be provided, and the digital receiver can be downsized. This can greatly contribute to lower prices.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of a wideband digital receiver according to the present invention.

FIG. 2 is a diagram illustrating the principle of frequency conversion according to the present invention.

FIG. 3 is a schematic configuration diagram showing an example of a conventional conventional wideband digital receiver.

FIG. 4 shows the input frequency of the 12-bit A / D converter versus ENO.
6 shows an example of characteristics of B and SNR.

[Explanation of symbols]

(Related to the present invention) 1. Antenna, 2. RF bandpass filter, 3. Low noise amplifier, 4. Mixer, 5.
Local oscillator, 6 IF bandpass filter,
7. IF amplifier, 8 A / D converter,
9. D / A converter, 10 sampling signal generator 11, low-pass filter, 12 A /
D converter, 13. Sampling signal generator,
14. DSP (Digital Signal Processor) (hereinafter referred to as the prior art) 21. Antenna, 22. RF bandpass filter, 23. Low noise amplifier, 24 ..
1st mixer, 25 ... first local oscillator, 26 ...
1st IF bandpass filter, 27 first IF signal amplifier, 28 second mixer, 29 second local oscillator, 30 second IF bandpass filter, 31
・ Second IF signal amplifier, 32 A / D converter, 3
3. Sampling signal generator, 34 DSP (Digi
tal Signal Processor)

Claims (1)

[Claims] A first A / D converter for converting an analog intermediate frequency signal into a digital signal; and a first A / D converter.
A D / A converter for converting the converter output into an analog signal;
A filter for limiting the band of the output frequency of the D / A converter, and a second A / D converter for converting the band-limited signal into a digital signal; By operating the D / A converter with a sampling signal generated by the same signal generator, the generation of error noise at the time of conversion due to the aperture jitter of the sampling signal is suppressed, and the frequency conversion is performed to perform the second conversion at a relatively low frequency. 2. A wideband digital receiver, wherein A / D conversion is performed by the A / D converter of item 2.