JPH0159775B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a device for converting an analog signal into a digital signal and a digital signal into an analog signal, and is applicable to voice band signals such as the audio field and communication field. Widely used in the field.

Configuration of the conventional example and its problems Figure 1 shows the configuration of the conventional example. Figure 1 shows an analog-to-digital converter (hereinafter referred to as ADC) using the adaptive delta modulation (hereinafter referred to as ADM) method.
FIG. This DAC has the features of simple configuration and low price.

The analog signal S1 input to input terminal 1 is
It is input to the (-) input terminal of analog comparator 2. Output D1 of this analog comparator 2
is input to flip-flop 3, and clock t
The signal is sampled and converted into a digital signal D2. The signal D2 is divided into two parts, one being output as the modulated output D3 of the ADM modulator to the output terminal 4, and the other being input to the adaptive step generator 5. The function of the adaptive step generator 5 is that when the modulation output D3 has the same sign continuously, for example, when four stages of commonly used flip-flops are connected in series, the functions are (+), (+), (+), Only the conditions of (+) or (-), (-), (-), (-) increase the adaptation step. The output signal S3 of the adaptive step generator 5 is input to an integrator 6 and converted into an analog signal S2. Analog signal S2
is input to the (+) input terminal of the analog comparator 2. The above is the configuration of the conventional example, but the second
The operation of this conventional example will be explained with reference to the drawings. FIG. 2 shows the waveforms of S1 and S2, which are the input signals of the analog comparator 2, with the horizontal axis representing time and the vertical axis representing voltage level. That is, when the analog signal S1 is input as a sine wave, the signal S2 follows the signal S1 and operates so as to minimize the difference M (the shaded part). Therefore, as shown in FIG. 2, the output signal D3 becomes a digital signal of level H in the interval _d0 - _d1 , level L in the interval _d1 - _d2 , and level H in the interval _d2 - _d3 .

This conventional example has a problem in that when the difference M between the input signals S1 and S2 is demodulated, it occurs as distortion, and the distortion is particularly large when the frequency is high and the input signal level is large.

OBJECTS OF THE INVENTION It is an object of the present invention to provide an analog-to-digital converter that solves the above problems, has less distortion, and can be constructed simply and at low cost.

Structure of the Invention The present invention includes a first branching means for dividing an analog signal into two, a first differential amplification means to which one of the outputs of the first branching means is inputted to a negative input terminal, and an inverted output equalizer means to which the other input is input, a second differential amplification means to which the output of the inverted output equalizer means is inputted to the positive input terminal, and an output of the first differential amplification means is inputted to the negative input terminal. an analog comparator; a memory means for sampling the output of the analog comparator using an external clock; and a second memory device that divides the output of the memory element into two and makes one the digital output of the analog-to-digital converter.
the other of the digital outputs of the branching means and the second branching means is inputted, and adaptive step generation means for adaptively generating an amplitude step value between one sample clock; and the output of the adaptive step generation means is inputted to an integrator. 1-bit analog-to-digital converting means for performing digital-to-analog conversion by performing digital-to-analog conversion; and third branching means for dividing the analog output of the 1-bit analog-to-digital converting means into two, one of the outputs of the third branching means being divided into two. While inputting it to the positive input terminal of the comparator, the other one is inputted to the negative input terminal of the second differential amplifier means, and the output of the second differential amplifier is connected so as to be inputted to the positive input terminal of the first differential amplifier. With this configuration, it is possible to have a simple configuration and also to reduce distortion.

DESCRIPTION OF EMBODIMENTS The present invention focuses on the fact that the ADM system has an analog signal output in addition to a digital signal output in the low frequency range of distortion that an analog-to-digital converter has, and reduces distortion used in conventional analog circuits. This is an application of countermeasures.

FIG. 3 shows an embodiment of the present invention.

In FIG. 3, the analog signal S11 input to the input terminal 1 is divided into two by the first branching means 7,
one to the (-) input terminal of the first differential amplifier 8,
The other one is input to the input terminal of the inverted output equalizer 9, respectively. The output S14 of the first differential amplifier 8 is
It is input to the (-) input terminal of analog comparator 2. Analog comparator 2 output D11
is input to flip-flop 3, and clock t
is sampled and converted into a digital signal D2. The signal D2 is divided into two by the branching means 3a, one of which is output to the output terminal 4 as the modulated output D13 of the ADM modulator, and the other is input to the adaptive step generator 5. The output signal S13 of the adaptation step 5 is input to an integrator 6 and converted into an analog signal S12. The output S12 of the integrator 6 is sent to the second branching means 9
divided into two by a, one side is connected to the (+) input terminal of the analog comparator, and the other side is connected to the second differential amplifier 11.
is input to the (-) input terminal.

On the other hand, the output signal S15 of the inverted output equalizer 9
is input to the (+) input terminal of the second differential amplifier 11 and outputs the output signal S16 of the second differential amplifier 11.
is input to the (+) input terminal of the first differential amplifier 8. Note that the portion of the conventional ADM modulator shown in FIG. 1 is shown surrounded by a dotted line 10. That is, in this embodiment, a two-channel differential amplifier and an inverted output equalizer are arranged before the analog comparator 2 of the conventional ADM modulator, and the analog input signal S1
1 and the output signal S12 of the conventional ADM modulator 10 are used as input signals for calculation.

With this configuration, distortion is reduced as shown by the following equation (1).

D′=1/(1/T)+A1・A2・D……(1) However, D′: Distortion improved in this example D: Distortion before improvement A1: Increased amount of first differential amplifier Amplitude A2: Amplification degree of the second differential amplifier T: Amplification degree of the conventional ADM circuit Since T is ideally 1, in order to reduce distortion, A1 and A2 should be increased.

On the other hand, in the conventional analog circuit distortion reduction measures described above, there is no need to consider time delay, but in this embodiment, a time delay is caused by the clock t. For example, if four stages of flip-flops 3 are connected in series and the clock is set to 250 kHz, the time delay amount will be 16 microseconds. However, if we convert this amount of time into a frequency, it becomes 60kHz, which is the upper limit of the audio band.
Since it is over 20kHz, it is not a problem.

Incidentally, the inverting equalizer 9 is necessary in order to match the frequency characteristics of the conventional ADM modulator 10.
Further, this embodiment can be applied to other 1-bit ADCs without using the ADM method.

Effects of the Invention The present invention can be configured easily and at low cost with little distortion, and is therefore necessary for digital signal processing in the audio field, electronic musical instrument field, so-called karaoke field, audio section in the video field, and communication field. It is possible to provide an analog-to-digital converter.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional analog-to-digital converter, FIG. 2 is an explanatory diagram of the same operation, and FIG. 3 is a block diagram of an analog-to-digital converter according to an embodiment of the present invention. 1...Input terminal, 2...Analog comparator, 3...Flip-flop, 3a, 7, 9a...
... Branching means, 4 ... Output terminal, 5 ... Adaptive step generator, 6 ... Integrator, 8 ... First differential amplifier, 9 ... Inverting output equalizer, 10 ... ADM
Modulator, 11... second differential amplifier.

Claims (1)

[Claims] 1. A first branching means that divides the analog signal into two, a first differential amplification means in which one of the outputs of the first branching means is inputted to the negative input terminal, and an inversion device in which the other output of the first branching means is inputted. an output equalizer means, a second differential amplification means to which the output of the inverted output equalizer means is input to the positive input terminal, an analog comparator to which the output of the first differential amplification means is input to the negative input terminal; storage means for sampling the output of the comparator using an external clock;
A second branching means divides the output of the memory element into two and makes one the digital output of the analog-to-digital converter, and the other of the digital outputs of the second branching means is input, and the amplitude step value between one sample clock is calculated. an adaptive step generation means for adaptively generating the step; a 1-bit analog-to-digital conversion means for performing digital-to-analog conversion by inputting the output of the adaptive step generation means to an integrator; and an analog output of the 1-bit analog-to-digital conversion means. 2
one of the outputs of the third branching means is inputted to the positive input terminal of the analog comparator, the other is inputted to the negative input terminal of the second differential amplification means, and the second An analog-to-digital converter configured by connecting the output of a differential amplifier to the positive input terminal of a first differential amplifier.