JP2000236276A - Broadband digital receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use a general A/D converter which is inexpensive and small-sized by making small the dynamic range that the A/D converter needs by compressing the signal level difference between an interference station and a desirable station with a logarithmic amplifier and inputting the result to the A/D converter. SOLUTION: A logarithmic amplifier 6 is additionally inserted between an IF band-pass filter 5 and an AGC amplifier 7, and an exponent expanding circuit 10 is further inserted between a channel separator 9 and a demodulator 11. Then the logarithmic amplifier 6 compresses and inputs the signal level difference between the interference station and desirable station to the A/D converter 8. In this receiver, the output signal of the channel separator 9 is logarithmically compressed by the logarithmic amplifier 6, so that the output signal, even if inputted to the exponent expanding circuit 10 and expanded in amplitude level by the circuit 10 is put back into a digital signal of the amplitude level. Then the demodulator 11 imposes modulation corresponding to the modulation system of a communication system to generate a data signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a small and inexpensive A / D converter for A / D conversion of a received signal in a wide band in a receiver used in digital mobile communication. Broadband digital receiver that can

[0002]

2. Description of the Related Art In recent years, with the development of digital circuit technology, examples of realizing functions realized by analog circuits by digital circuits are increasing. When the functions are realized by digital circuits, there is no variation in characteristics, no aging,
The advantage that no adjustment is required is obtained. Furthermore, when a programmable device such as a DSP is used as a digital circuit, the function is described by software, so that there is an advantage that modification and change are easy. In the field of mobile communications such as digital cellular phones, the transition to digital circuits is progressing. As an ultimate example, software radios (Joe Mitola, "The Software Radio Archi
tecture ", IEEE Communication Magazine May1995 Vol.3
3 No. 5) has been proposed.

FIG. 5 is a schematic diagram showing an example of a conventional wideband digital receiver in which channel separation generally performed by an analog circuit is performed by a digital circuit. The broadband digital receiver is a receiver that performs A / D conversion of a received wideband signal as it is in an RF band or an IF band, and performs processing after channel separation by a digital circuit. (Related patent: "Digital Radio Frequency Receiver" Japanese Patent Application No. 61-504791) As shown in the figure, this receiver comprises an antenna 1 for receiving radio waves, and an RF bandpass filter 2 for band limitation. , A local signal oscillator 4, a mixer 3, an IF band-pass filter 5 for converting the frequency of an IF signal and performing band limitation, and an A signal for amplifying the IF signal.
A GC amplifier 7, an A / D converter 8 for converting an analog received signal into a digital signal, a channel separator 9 for separating a desired channel band, and a demodulator 11 for demodulating a data signal from the output signal of the channel separator. It consists of.

In FIG. 5, a received signal received by an antenna 1 is input to an RF band-pass filter 2 and subjected to necessary band limitation. Here, the necessary band is a bandwidth receivable by the present wideband digital receiver, and is set so as to match a service band band of a normally used system. For example, a PDC 800 MHz mobile phone system has a bandwidth of 16 MHz. Here, the pass band width of the RF bandpass filter 2 is W.
Next, the received signal subjected to the band limitation by the RF bandpass filter 2 is subjected to frequency conversion and band limitation by the mixer 3, the local oscillator 4, and the IF bandpass filter 5, and becomes an IF signal. The bandwidth of the IF bandpass filter 5, that is, the bandwidth of the IF signal is W, which is the same as that of the RF bandpass filter. The IF signal is amplified by an AGC amplifier 7 and then converted into a wideband digital signal by an A / D converter 8. The amplification factor of the AGC amplifier 7 is feedback-controlled so that the input signal to the A / D converter 8 becomes maximum within a range not exceeding the maximum input level of the A / D converter 8. The wideband digital signal is supplied to a channel separator 9.
And is separated into a desired narrow band (channel band) digital signal. Narrow band here (channel band)
For example, in a PDC 800 MHz mobile phone system, the bandwidth is 25 kHz. The narrow-band (channel band) digital signal separated from the channel is demodulated by the demodulator 11 in accordance with the modulation scheme of the system (π / 4 QPSK for a PDC 800 MHz mobile phone) to become a data signal.

[0005] In a base station of a mobile communication system, the positional relationship between a plurality of mobile terminal stations usually changes from moment to moment. The ratio of the input signal levels can be very large. Therefore, it is necessary that the circuits of each part of the receiver have a sufficient dynamic range. If the interfering station is near the receiver and the desired station is far, for example, FIG.
As shown in the figure, in the spectrum of the input signal of the A / D converter 8, the level difference between the received signals from both stations is large. In this example, the interference station signal level is 70 dB higher than the desired station signal level. When the signal of this level difference is A / D converted to demodulate a desired station signal, the A / D converter 8 must have at least 80 in consideration of a margin for demodulation.
A dynamic range of dB is required.

[0006]

However, usually,
The above 80 dB dynamic range is converted into 14 bits when converted into the number of bits for A / D conversion. Sampling speed required for wideband digital receiver (several MHz ~
At present, A / D converters having a dynamic range of as large as 14 bits at several tens of MHz have a disadvantage that they are very expensive, large, and consume a large amount of current. The present invention has been made to solve the above problems,
The dynamic range (number of bits) required for the A / D converter is reduced without deteriorating performance.
Moreover, it is an object of the present invention to provide a wideband digital receiver that can use an A / D converter with low current consumption.

[0007]

In order to solve the above problems, according to the first aspect of the present invention, there is provided an AGC amplifier for amplifying a wideband received signal, and an analog / digital converter for digitally converting an output signal of the AGC amplifier. A wideband digital receiver comprising: a conversion unit; a channel separation unit for separating a desired channel band from an output of the analog / digital conversion unit; and a demodulation unit for demodulating an output signal of the channel separation unit. Logarithmic amplification means for logarithmically compressing the amplitude level of the received signal is provided before the means, and exponential expansion means for exponentially expanding the amplitude level of the output of the channel separation means is provided before the demodulation means. According to the second aspect of the present invention, an AGC amplifier for amplifying a wideband received signal, an analog / digital converter for digitally converting an output signal of the AGC amplifier, and an output from the analog / digital converter are provided. Sample interpolating means for interpolating a sample of an output signal of said analog / digital converting means in a wideband digital receiver comprising a channel separating means for separating the channel band of the above and a demodulating means for demodulating an output signal of said channel separating means. Digital / analog conversion means for converting the output of the sample interpolation means into an analog signal, subtraction means for subtracting the output of the AGC amplification means from the analog signal, and a second means for amplifying the output of the subtraction means. Digitally converting the output signal of the second AGC amplifying means and the second AGC amplifying means. A second analog / digital conversion means for switching is connected before the channel separation means.

[0008]

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 diagram showing a configuration of an embodiment of a broadband digital receiver according to the present invention. As shown in FIG. 1, the receiver includes an antenna 1 for receiving a radio wave, an RF bandpass filter 2 for band limitation, a local signal oscillator 4 for frequency-converting an IF signal and band limiting. 3 and IF
A bandpass filter 5, a logarithmic amplifier 6 for logarithmically compressing the amplitude level of the input signal, an AGC amplifier 7 for amplification,
A / D converter 8 for converting an analog received signal to digital, and channel separator 9 for separating a desired channel band
And an exponent expansion circuit 10 for expanding the amplitude level of the output signal of the channel separator to a level before compression, and a demodulator 11 for demodulating a data signal from the output signal of the exponent expansion circuit 10.

The wideband digital receiver having the above-described configuration according to the present invention comprises a logarithmic amplifier 6 between an IF bandpass filter 5 and an AGC amplifier 7 in the conventional receiver shown in FIG.
Further, an exponential expansion circuit 10 is additionally inserted between the channel separator 9 and the demodulator 11, and the other common parts operate with the same functions as in FIG.
The operation of the receiver will be described below in detail, focusing on the operation of the logarithmic amplifier 10 and the exponential expansion circuit 11. FIG.
, The wideband received signal received by the antenna 1 and converted to the IF signal by the mixer 3 is (PDC 800 MHz)
After being band-limited by an RF bandpass filter 5 having a bandwidth of 16 MHz and a pass bandwidth W, the signal is input to a logarithmic amplifier 6. Considering the case where the interfering station presents a spectrum as shown in FIG. 6 and the desired station is far away from the receiver, the level ratio of these two signals is ideally calculated by the logarithmic amplifier 6 by the following equation. Compressed. (Level ratio after compression) = 10 log (Level ratio before compression) FIG. 2 is a diagram showing the spectrum of the output signal of the logarithmic amplifier 6, in which the level ratio between the interference signal and the desired signal is compressed to 20 dB.

The signal logarithmically compressed as described above is called AG
Output to the C amplifier 7. The amplification factor of the AGC amplifier 7 is feedback-controlled so that the input signal to the A / D converter 8 does not exceed the maximum input level of the A / D converter 8. The signal amplified by the AGC amplifier 7 is input to an A / D converter 8 and converted into a digital signal. Further, the channel separator 9 converts the digital signal into a desired narrow-band (channel band) digital signal (for a PDC 800 MHz portable telephone). (25 kHz bandwidth). Since the output signal of the channel separator 9 is logarithmically compressed by the logarithmic amplifier 6, it is input to the exponential expansion circuit 10,
The exponent expansion circuit 10 expands the amplitude level and returns the digital signal to the original amplitude level. afterwards,
In the demodulator 11, the modulation method (PDC80) of the communication system is used.
The signal is demodulated in accordance with (π / 4QPSK for a 0 MHz type mobile phone) and becomes a data signal.

In the above operation, the level ratio between the interfering station signal and the desired station signal input to the A / D converter 8 is compressed to 20 dB, and a margin in the exponent expansion circuit 10 and the demodulation circuit 11 is taken into consideration. The A / D converter 8 only needs to have a dynamic range of 40 dB. When the dynamic range of 40 dB is converted into the number of bits in the A / D conversion, it becomes 7 bits. Number M required for wideband digital receiver
An A / D converter having a sampling rate of Hz to several tens of MHz and satisfying the above dynamic range includes, for example, a general-purpose 8-bit A / D converter that is inexpensive, small, and consumes little current.
A D converter can be used. In the above-described embodiment, the logarithmic amplifier 6 is disposed immediately before the AGC amplifier 7. However, the logarithmic amplifier 6 may be disposed at any position after the band-pass filter 2 before the AGC amplifier. The circuit 10 can also be arranged immediately before the channel separator 9.

FIG. 3 is a schematic diagram showing an embodiment of the wideband digital receiver according to the second aspect of the present invention. As shown in FIG. 1, the receiver includes an antenna 1 for receiving a radio wave, an RF bandpass filter 2 for band limitation, a local signal oscillator 4 for frequency-converting an IF signal and band limiting. 3, an IF bandpass filter 5, an AGC amplifier 7 for amplification, an A / D converter 8 for converting an analog reception signal into a digital signal,
A sample interpolation circuit 12 for performing sample interpolation of an output signal of the D converter 8, a D / A converter 13 for converting a digital signal after sample interpolation into an analog signal, a low-pass filter 14 for removing an image signal, and the AGC A subtractor 15 for extracting a level difference between an output signal of the amplifier 7 and an output signal of the low-pass filter 14, a second AGC amplifier 16 for amplification, and a second A / D for converting an analog reception signal into a digital signal. It comprises a converter 17, a channel separator 9 for separating a desired channel band, and a demodulator 11 for demodulating a data signal from the output signal of the channel separator.

In the wideband digital receiver having the above configuration, the wideband received signal is converted into an IF signal, amplified by an AGC amplifier 7 and converted into a digital signal by an A / D converter 8. Wideband IF converted to digital signal
The signal is input to the sample interpolation circuit 12 and undergoes sample interpolation. As a result, the sample rate and digital signal data resolution of the output signal of the sample interpolation circuit 12 are improved. As a method of sample interpolation, for example, linear interpolation with a small processing amount can be used. 4A is a spectrum diagram of an input signal of the A / D converter 8 when the interference station is near and the desired station is far, and FIG. 4B is a diagram showing the D / A. FIG. 3 is a spectrum diagram of an output signal of a converter 13. As shown in FIG.
The interfering station signal level of the received signal is much higher than the desired station signal level. Since the gain of the AGC amplifier 7 is feedback-controlled so as not to exceed the maximum input level of the A / D converter 8, if the dynamic range of the A / D converter 8 is small, the desired station is controlled. The signal is canceled out by the quantization noise. As a result, the output of the A / D converter 8 contains only the interference station signal and the quantization noise. The output signal of the A / D converter 8 is
The data is input to the sample interpolation circuit 12 and sample interpolation is performed. This signal is output to the D / A converter 13 after the quantization noise signal is suppressed by sample interpolation. Therefore, the analog output signal from the D / A converter 13 is an interference station signal and a suppressed quantization noise signal. However, the D / A converter 13 must be compatible with the sample rate and the resolution (number of quantization bits) after sample interpolation. The output signal of the D / A converter 13 is input to a low-pass filter 14 where an image signal is removed, and then output to a subtractor 15.

FIG. 4B shows the low-pass filter 14.
A replica of the interference station signal having a large dynamic range can be obtained from the spectrum diagram of the analog signal output from the CDMA. An output signal of the low-pass filter 14 and an input signal of the A / D converter 7 (an output signal of the AGC amplifier 7) are input to the subtractor 15, and a signal representing a difference between the two signals, that is, FIG. As shown in), it is possible to obtain a signal in which only the interference station signal among the input signals of the A / D converter is suppressed. Since only the interfering station signal is suppressed in the subtracter output signal, the desired station signal is amplified by the second AGC amplifier 16 and is not eliminated by the quantization noise. At 17, it is converted back to a digital signal. The amplification factor of the second AGC amplifier 16 depends on the input signal to the second A / D converter 17.
The feedback control is performed so that the maximum input level does not exceed the maximum input level 7. The wideband digital signal converted into the digital signal is further processed by a channel separator 8 into a desired narrow band (channel band) digital signal (PDC).
In the case of an 800 MHz mobile phone, the bandwidth is separated to 25 kHz, and the output signal of the channel separator 8 is demodulated by a demodulator 9.
Is demodulated according to the modulation system of the communication system (π / 4QPSK in the case of a PDC 800 MHz mobile phone), and becomes a data signal.

As described above, the receiver of the present invention performs A / D conversion after suppressing the interfering station signal, so that the dynamic range required for the A / D converter can be small, which is smaller than the conventional system. Inexpensive and small A with small number of quantization bits
It can be configured using a / D converter. On the other hand, a D / A converter with a high speed and a large number of quantization bits is required.
However, compared with the A / D converter, the D / A converter is easy to increase the speed and the number of quantization bits, and even if the number of constituent circuits including the D / A converter is taken into consideration, the receiver is not required. This is advantageous in reducing the size and cost of the device.

[0016]

As described above, in the wideband digital receiver according to the first aspect, the signal level difference between the interfering station and the desired station is compressed by the logarithmic amplifier and input to the A / D converter. Therefore, the dynamic range required for the A / D converter can be reduced, and an inexpensive and compact general-purpose A / D converter can be used. In the wideband digital receiver according to the present invention, the interfering station signal is sample-interpolated to extract the interfering station signal and the suppressed quantization noise signal level, and the signal before the sample interpolation and the signal after the interpolation are sampled. By subtraction with
Since a wideband signal in which only the signal of the interfering station is suppressed is input to the A / D converter, the dynamic range required for the A / D converter can be reduced. An A / D converter can be used. Therefore, compared to the conventional wideband digital receiver,
There is a remarkable effect that cost and current consumption can be greatly reduced and miniaturization can be greatly promoted.

[Brief description of the drawings]

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

2 is a logarithmic amplifier 6 of the wideband digital receiver of FIG.
Output signal spectrum of.

FIG. 3 is a schematic configuration diagram showing one embodiment of a wideband digital receiver according to the invention of claim 2;

4 (a) is a spectrum of a signal of each part of the wideband digital receiver of the invention of FIG. 3, (a) is a spectrum of an input signal of the A / D converter 8, and (b) is an output of the D / A converter 13. (C) is the spectrum of the signal input to the A / D converter 17.

FIG. 5 is a schematic configuration diagram showing an example of a conventional wideband digital receiver.

FIG. 6 shows the input signal spectrum of the A / D converter 8 when the interference station is near and the desired station is far.

[Explanation of symbols]

1. Antenna, 2. RF bandpass filter,
3 ・ ・ Mixer 、 4 ・ ・ Local signal oscillator 、
5 IF bandpass filter, 6 Logarithmic amplifier according to the present invention, 7 AGC amplifier, 8 A / D
Converter, 9 channel separator, 10
.. exponential expansion circuit according to the present invention, 11 demodulator, (hereinafter referred to as the present invention) 12. sample interpolator, 13. D / A converter, 14. low-pass filter, 15. subtraction Device, 16 second AGC amplifier, 17 second A / D converter

Claims (2)

[Claims] An AGC amplifier for amplifying a wideband received signal, an analog / digital converter for digitally converting an output signal of the AGC amplifier, and a desired channel band separated from an output of the analog / digital converter. In a wideband digital receiver comprising a channel separating means for performing the above and a demodulating means for demodulating an output signal of the channel separating means, a logarithmic amplifying means for logarithmically compressing the amplitude level of the received signal is provided at a stage preceding the AGC amplifying means,
A broadband digital receiver, comprising: an exponential extension unit for exponentially extending the amplitude level of the output of the channel separation unit at a stage preceding the demodulation unit. 2. An AGC amplifier for amplifying a wideband received signal, an analog / digital converter for digitally converting an output signal of the AGC amplifier, and a desired channel band separated from an output of the analog / digital converter. And a sample interpolator for performing a sample interpolation on an output signal of the analog / digital conversion means in a wideband digital receiver comprising a channel separation means for performing demodulation of an output signal of the channel separation means. Digital / analog conversion means for converting the output of the means into an analog signal, subtraction means for subtracting the output of the AGC amplification means from the analog signal, and second AGC amplification means for amplifying the output of the subtraction means. A second analog for digitally converting an output signal of the second AGC amplifying means. And digital conversion means,
A wideband digital receiver connected before the channel separating means.