JPH07312552A - D/a converter - Google Patents

Abstract

PURPOSE:To facilitate large scale integration, to make the D/A converter small and to decrease power consumption by adopting simple circuit configuration comprising a correction pulse generating circuit generating a desired correction pulse in response to a clock signal and multiplier only so as to correct deterioration in amplitude due to the aperture effect. CONSTITUTION:An n-bit digital signal is applied to a digital signal input terminal 1 and given to a D/A converter 2. An output of the circuit 2 is a PAM signal pulse train whose analog property duty factor is 100% and the period of which is matched with that of a clock signal CLK. Thus, a frequency characteristic of the PAM signal being the output of the circuit 2 is a characteristic in which Fourier transformation of each isolated rectangular pulse of the PAM signal is applied to the frequency characteristic of a source analog signal. On the other hand, a correction pulse output with a prescribed waveform is generated from a correction pulse generating circuit based on an output of a clock signal generator 3 and given to a multiplier 5. The deterioration in the amplitude due to aperture effect is corrected through the multiplication of an output of the circuit 2 by the correction pulse.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a DA converter (digital-analog converter) for converting a digital signal into an analog signal.

[0002]

2. Description of the Related Art In the latest electronic equipment, the development of digital technology is so remarkable that all signal processing is performed by digital signal processing. But, as we all know,
Usually, audio signals, video signals, etc., which are naturally generated, are obtained as analog signals. Therefore, in order to perform signal processing with a digital signal, first, it is necessary to convert an analog signal into a digital signal. For that purpose, an AD converter (analog-digital converter) is used, and the result of digital signal processing is A DA converter is used to convert back to an analog signal. Further, in order to perform signal processing of audio signals, video signals and the like with the AD converter and the DA converter, it is well known that "an analog signal such as an input audio signal or video signal has a frequency higher than the frequency f _0. In the case of a signal that does not include (a band-limited signal), the original signal can be reproduced from the pulse train by performing sampling with a pulse train whose repetition frequency is greater than 2f ₀ , according to Nyquist's theorem Basically, signal processing is performed. However, when signal processing is performed according to the Nyquist theorem, there is a problem that distortion occurs.

A DA converter according to the prior art will be described with reference to FIGS. FIG. 2 shows a block diagram of the most basic DA converter for converting a digital signal into an analog signal. In FIG. 2, 1 is an input terminal for a digital signal for converting into an analog signal, 2 is a DA converter for converting a digital signal into an analog signal, and 3 is a clock signal for generating a clock signal having a cycle matching the sampling cycle of the digital signal. Generator, 7 is DA converter 2
Aperture distortion correction filter for correcting the distortion of the signal output from the device, and reference numeral 6 denotes an output terminal of the analog signal converted from the digital signal and having the distortion corrected.

FIG. 3 is a diagram showing a relationship between an analog signal converted from a digital signal by a DA converter and outputted and an original analog signal before being digitized, where a is an original analog signal and b is a DA conversion. , CLK is a clock signal, and T is a cycle of the clock signal. FIG. 4 is a diagram showing a frequency characteristic of an analog signal converted from a digital signal by a DA converter and output.

The operation of the DA converter according to the prior art will be described. In FIG. 2, digital signal input terminal 1
Is applied with an n-bit digital signal and is input to the DA converter 2. At this time, the clock signal generator 3 inputs to the DA converter 2 a clock signal having the same sampling cycle as the input digital signal. DA to which n-bit digital signal and clock signal are input
The converter 2 converts the digital signal into an analog signal in accordance with the cycle of the clock signal and outputs the analog signal to the aperture distortion correction filter 7. Aperture distortion correction filter 7
The analog signal input to is an analog signal whose aperture distortion has been corrected and is output from the output terminal 6. The analog signal output from the DA converter 2 is generally called an analog signal, but normally, as shown in FIG. 3, a PAM (pulse amplitude modulation) having a duty of 100% and having an analog property in which the cycle matches the clock signal CLK. ) Signal pulse train b
Becomes Now, let us consider the frequency characteristic of the output signal of the DA converter 2.

According to the Nyquist theorem, the original analog signal a shown in FIG.
T, fs: sampling frequency) or less, the frequency characteristic of the output PAM signal b of the DA converter 2 becomes a signal that repeats for each sampling frequency as shown in FIG. PAM shown in 3
The characteristic is obtained by subjecting each isolated rectangular pulse of the signal b to the Fourier transform. Since the amplitude deterioration of the high frequency component due to the characteristic of the Fourier transform of this isolated rectangular pulse (the dotted line portion shown by a ′ in FIG. 4 is the spectrum when the aperture effect is not received), the Nyquist frequency (fs / 2)
The signal components in the vicinity are degraded by about 4 dB. Further, the signal components above the Nyquist frequency are also deteriorated according to the characteristics of the aperture effect. Therefore, especially when the frequency component of the original analog signal before being converted into a digital signal extends to near the Nyquist frequency and the frequency component is required, or in the device after the DA converter, the harmonic component due to sampling is positively applied. 2 is used, it is indispensable to perform the amplitude deterioration correction using the aperture distortion correction filter 7 or the like as shown in FIG.

As described above, the amplitude distortion correction is performed by using the aperture distortion correction filter after the DA converter.
A case of a wireless device will be described as an example of positively utilizing the higher harmonic component due to sampling in a device after the DA converter. In the case of a radio device based on digital signal processing, the output of the DA converter is usually frequency-converted to a radio frequency for use. Therefore, when performing the frequency conversion, spurious characteristics required for the communication device, an intermediate frequency filter and a high frequency filter are used. Due to the characteristics and the like, the double superheterodyne system, and in some cases, the triple superheterodyne system shown in FIG. 5 is often used. FIG. 5 is an explanatory diagram of the triple superheterodyne system, and shows an intermediate frequency stage and a high frequency stage after the DA converter. In FIG. 5, the output of the DA converter 10 passes through the mixing circuits 11, 13, 15 and the bandpass filters 12, 14, 16 into which the signals of the local oscillation frequency are input, respectively, and becomes an intermediate frequency and a high frequency, and from the antenna 17. Sent.

Here, in consideration of size reduction and power consumption reduction by reducing the number of parts, it is desired that the frequency conversion is performed as few times as possible. Further, if the frequency conversion is small, the intermediate frequency before frequency conversion becomes high, and there is an advantage that the design of the high frequency (intermediate frequency) filter for spurious suppression in the subsequent stage becomes easy. Therefore, it is desirable that the output frequency of the DA converter is a high frequency as close to the radio frequency as possible in order to reduce the number of frequency conversions of the subsequent circuit. However, conversely, in order to reduce the price and power consumption of the DA converter, it is necessary to keep the frequency of the output of the DA converter as low as possible. In order to meet these contradictory requirements, it is necessary to positively utilize the harmonic components of the output signal of the DA converter, and as described above, it is inevitably necessary to correct the deterioration due to the aperture effect. come. As a conventional technique for compensating for the characteristic deterioration in the output signal of the DA converter, for example, JP-A-60-187133 and JP-A-63-245 are known.
No. 129 publication is known. Among them, the above-mentioned JP-A-6
JP-A 0-187133 discloses a step between a staircase wave F (t) obtained as a DA-converted output and a staircase wave F (t-T) whose phase is delayed from the staircase wave F (t) by a sampling period T. F
K {F obtained by multiplying (t) -F (t-T) by a predetermined coefficient k
By providing a correction means for adding (t) -F (t-T)} to the F (t), characteristic deterioration due to the aperture effect is corrected. Further, the above-mentioned JP-A-63-24
Japanese Patent No. 5129 is a DA converter intended mainly to reduce the phase distortion of an output signal by multiplying digital data by a unit pulse response signal and synthesizing and accumulating the multiplication results by adding means. .

[0009]

However, the DA converter according to the prior art described above has the following problems. (A) In the DA converter shown in FIG. 2, since the analog filter is used as the aperture distortion correction filter for correcting the characteristic deterioration due to the aperture effect, the circuit scale becomes large, the device becomes large, and the cost is increased. It was causing the problem of rising. In addition, there is a drawback that the circuit must be changed to a circuit that matches the frequency range depending on which frequency range is to be corrected. (B) Similarly, in the DA converter disclosed in the above-mentioned Japanese Patent Laid-Open No. 60-187133, analog delay means, first and second analog addition means, and analog multiplication means are indispensable as the configuration of the correction circuit. Therefore, the circuit scale becomes large, which causes problems such as an increase in size of the device and an increase in cost. (C) The DA converter described in Japanese Patent Laid-Open No. 63-245129 uses a multiplication type DA converter (MDAC) to multiply digital data by a digital weighting coefficient, and the multiplication result (analog ) Is accumulated by a summing amplifier. That is, it has a configuration of a transversal filter (or FIR filter) whose input is a digital signal and whose output is an analog signal. Therefore, in order to correct the aperture effect with such a configuration,
As with a normal filter, frequency correction is performed to increase the high frequency gain. However, since the signal processing in this DA converter is completely linear processing, there is a problem in that a signal above the Nyquist frequency cannot be handled.

The present inventor has studied the correction of the aperture effect of the DA converter, and as a result, by multiplying the output signal of the DA converter by a predetermined correction pulse, a Nyquist circuit is used. It is possible to correct the aperture effect in a desired frequency band including frequencies higher than the frequency. It is a first object of the present invention to provide a DA converter capable of correcting amplitude deterioration due to the aperture effect in a desired frequency band including frequencies higher than the Nyquist frequency with a simple circuit configuration. A second object of the present invention is to provide a DA converter capable of correcting the amplitude deterioration of the high frequency component due to the aperture effect and utilizing the harmonics appearing by sampling.

[0011]

In order to achieve the first and second objects, a DA converter of the present invention has a DA converter and an aperture distortion correction circuit, and a digital signal according to a cycle of a clock signal. The DA converter for correcting the aperture distortion of the converted analog signal is provided with an aperture distortion correction circuit having a correction pulse generation circuit and a multiplier. Further, in detail, the DA converter of the present invention is
The present invention is provided with a correction pulse generation circuit that has a cycle of a clock signal and generates a correction pulse of an arbitrary duty and amplitude, and that combines two pulses that have a cycle of the clock signal and have arbitrary duty and amplitude. Is provided with a correction pulse generating circuit for generating a correction pulse.

[0012]

The DA converter is a DA converter which has a DA converter and an aperture distortion correction circuit and performs aperture distortion correction on an analog signal obtained by converting a digital signal in accordance with the cycle of a clock signal. An aperture distortion correction circuit having a multiplier corrects the aperture distortion of the analog signal output from the DA converter. Further, in more detail, a correction pulse generating circuit that generates a correction pulse having a cycle of a clock signal and having an arbitrary duty and amplitude DA
Corrects the aperture distortion of the analog signal output from the converter. Further, the aperture distortion of the analog signal output from the DA converter is corrected by a correction pulse generation circuit that generates a correction pulse by combining two pulses that have the cycle of the clock signal and have arbitrary duty and amplitude.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the DA converter according to the present invention will be described with reference to FIGS. FIG. 1 shows a block diagram of a DA converter according to the present invention for converting a digital signal into an analog signal. In FIG. 1, 1 is an input terminal of a digital signal for converting into an analog signal, 2 is a DA converter for converting a digital signal into an analog signal, and 3 is a clock signal for generating a clock signal having a cycle matching the sampling cycle of the digital signal. A generator (3 may be used as a clock signal input terminal and a clock signal having a cycle matching the sampling cycle may be input from an external clock signal generator) 4 is a correction pulse having a clock signal as an input signal The generation circuit 5 is a multiplier which receives the analog signal output from the DA converter 2 and the correction pulse signal output from the correction pulse generation circuit 4, and 6 is an analog signal converted from the digital signal and corrected. Indicates the output terminal. FIG. 6 shows waveforms at various parts of the DA converter shown in FIG. In FIG. 6, (a) is the output signal of the DA converter 2, (b) is the clock signal output from the clock signal generator 3, (c) is the correction pulse output from the correction pulse generation circuit 4, and (d) ) Is D output from the multiplier 5
The output signal of the A converter 2 is a corrected output signal.

Next, the operation will be described. In FIG. 1, an n-bit digital signal is applied to the digital signal input terminal 1 and input to the DA converter 2. DA at this time
The converter 2 is supplied with the clock signal shown in FIG. 6B having the same sampling cycle T as the input digital signal from the clock signal generator 3. In the DA converter 2 to which the n-bit digital signal and the clock signal having the same sampling period T as that of the digital signal are input, the digital signal is converted into the digital signal shown in FIG.
Is converted into an analog signal and output to the multiplier 5. As described above, the analog signal shown in FIG. 6A output from the DA converter 2 has a 100% duty PAM having an analog property in which the cycle is the same as that of the clock signal CLK shown in FIG. 6B. It is a signal pulse train. Therefore, as described above, the frequency characteristic of the output PAM signal of the DA converter 2 is a characteristic obtained by applying the Fourier transform of each isolated rectangular pulse of the PAM signal to the frequency characteristic of the original analog signal.

On the other hand, the clock signal output from the clock signal generator 3 is also sent to the correction pulse generation circuit 4, and the correction pulse generation circuit 4 has a predetermined waveform according to the input clock signal (see FIG. 6). The correction pulse shown in c) is generated and output to the multiplier 5. The correction pulse generation circuit 4 generates a plurality of pulses according to the input clock signal and synthesizes the plurality of pulses to generate a correction pulse. FIG. 6C shows an example of the correction pulse, which has a period T and a pulse width W = T / 2 (duty 50
%), And an example of a pulse signal with an amplitude of ± 1 is shown. Figure 6
Details of the correction pulse shown in (c) will be described with reference to FIG. 7. The correction pulse shown in FIG. 6C is a series of correction pulses (c) shown in FIG. 7. The correction pulse (c) shown in FIG. 7 is the same as the pulse shown in FIG.
It is generated by synthesizing the pulse of (b).

As shown in FIG. 7D, the Fourier transform of each pulse shown in FIGS. 7A, 7B and 7C shows that the pulse (a) has a frequency characteristic i and the pulse (b) has a frequency characteristic j. The correction pulse (c) obtained by combining the pulses (a) and (b) can be expressed as the frequency characteristic k. Therefore, the pulses (a) and (b) are
A correction pulse (c) having an arbitrary frequency characteristic can be obtained by changing the duty and the amplitude of and combining them. The correction pulse shown in FIG. 6C is output to the multiplier 5 as the output signal of the correction pulse generating circuit 4, and the output signal of the DA converter 2 is multiplied to output the output signal as shown in FIG. 6D. The analog signal output terminal 6 is used to change the frequency characteristics of the
Can be output from. For example, if the frequency characteristic of the correction pulse is k in FIG. 7D as described above, for example, the period T = 50 ns (clock frequency 1 / T
= 20 MH), the frequency band in which the amplitude deterioration due to the aperture effect can be corrected is 1 / (5/4 · T) = 25 M
It will be in the vicinity of Hz.

As an example of performing the amplitude deterioration correction using the aperture distortion correction circuit having the correction pulse generation circuit and the multiplier according to the present invention and positively utilizing the harmonic component due to sampling in the device after the DA converter. The case of a wireless device will be described. FIG. 8 shows a double superheterodyne system for the intermediate frequency stage and the high frequency stage using the DA converter according to the present invention. In FIG.
The output of the DA converter 20 passes through the mixing circuits 21 and 23 and the bandpass filters 22 and 24 to which the signals of the local oscillation frequency are input, and becomes an intermediate frequency and a high frequency,
It is amplified by the high frequency power amplifier 25 and transmitted from the antenna 26. When a concrete frequency is shown in the device shown in FIG. 8 assuming an FM transmitter, the clock signal of the DA converter is 8.56 MHz, and the local frequency of the signal input to the mixing circuit 21 is as shown in FIG. The transmission frequency is 10.7 MHz, and the local transmission frequency of the signal input to the mixing circuit 23 is 65.3 to
It becomes a specific frequency of 79.3MHz, 76-90MHz
The specific frequency of is obtained, the power is amplified and transmitted. Normal,
When the DA converter output is used, the signal frequency after conversion into an analog signal is limited by the Nyquist frequency fs / 2 (fs: sampling frequency). Naturally, the higher the analog signal frequency, the higher the clock of the DA converter. The signal (sampling frequency) becomes high. But,
By performing aperture distortion correction as shown in the present invention, fs
Since analog signals of frequencies around can be reproduced and used,
If the frequencies of the analog signals to be reproduced are the same, when the present invention is used, the clock signal frequency can be significantly reduced, and high accuracy and low power consumption can be achieved.

[0018]

According to the present invention, since the amplitude deterioration due to the aperture effect can be corrected with an extremely simple circuit configuration of only a correction pulse generating circuit for generating a desired correction pulse in accordance with a clock signal and a multiplier, the LSI can be corrected. It is also easy to make the device smaller, the cost can be reduced, the power consumption can be reduced, and the reliability can be improved. Further, in the present invention, since the multiplication processing (non-linear processing) of the waveform is performed in the multiplication processing, the spectrum moves and it is possible to handle a signal having a Nyquist frequency or higher. Therefore, it is possible to realize a DA converter capable of correcting the amplitude deterioration due to the aperture effect in a desired frequency band. Further, by correcting the amplitude deterioration of the high frequency component due to the aperture effect, it is possible to use the harmonics that appear due to sampling. Therefore, especially in a device such as a wireless device that needs to be converted into a high frequency by a post-stage circuit of a DA converter , The latter stage circuit of the DA converter can also be simplified, and the effect is remarkable.

[Brief description of drawings]

FIG. 1 is a block diagram of a DA converter according to the present invention.

FIG. 2 is a block diagram of a DA converter according to the related art.

FIG. 3 is a diagram illustrating a relationship between an output signal of a DA converter and an original analog signal.

FIG. 4 is a diagram illustrating output signal frequency characteristics of a DA converter.

FIG. 5 is an explanatory diagram of a wireless device having a DA converter according to the related art.

FIG. 6 is a waveform diagram of each part of the DA converter according to the present invention.

FIG. 7 is a diagram for explaining the generation and frequency characteristics of a correction pulse generated in the correction pulse generation circuit of the DA converter according to the present invention.

FIG. 8 is an explanatory diagram of a wireless device having a DA converter according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Digital signal input terminal, 2 ... DA converter, 3 ... Clock signal generator, 4 ... Correction pulse generation circuit, 5 ... Multiplier, 6 ... Analog signal output terminal, 7 ... Aperture distortion correction filter, 10 ... DA Conversion device, 11, 13, 15,
21, 23 ... Mixing circuit, 12, 14, 16, 22, 24
… Band pass filters, 17, 26… Antennas, 20…
DA converter, 25 ... High-frequency power amplifier.

Claims (3)

[Claims] 1. A DA converter that has a DA converter and an aperture distortion correction circuit, and performs aperture distortion correction on an analog signal obtained by converting a digital signal in accordance with the cycle of a clock signal. A DA converter having an aperture distortion correction circuit provided therein. 2. The DA converter according to claim 1, further comprising a correction pulse generation circuit which generates a correction pulse having a cycle of a clock signal and having an arbitrary duty and amplitude. 3. The apparatus according to claim 1, wherein the duty cycle and the amplitude are arbitrary and have a cycle of a clock signal.
A DA converter comprising a correction pulse generation circuit for generating a correction pulse by combining two pulses.