JPS6376618A - Da converter system - Google Patents

Abstract

PURPOSE:To reproduce only the difference in phase by providing a phase inverting circuit between a pulse density modulator and an analog low pass filter. CONSTITUTION:The system is composed of a pulse density modulating system DA converter 111 having a phase inverting function and an analog low pass filter 112 to rectify an output PDM signal Y' and convert it to an analog signal Z. Since the DA converter 111 outputs selectively a PDM signal Y or an inverting signal Y to the Y' and executes the phase inversion based on a phase inverting signal PI together with a pulse density modulator 113 to convert a PCM signal X supplied from a digital signal processing device 12 to the PDM signal Y, the quality deterioration at the analog system after the DA converter is eliminated.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a DA converter system used in digital audio equipment, communication equipment, measuring equipment, etc., and particularly relates to a DA converter system having a phase inversion function. system.

<Conventional technology> Conventionally, when inverting the phase of an analog signal in a digital signal processing system (digital audio equipment, etc.), the method for inverting the phase of the analog signal is to switch the inverting analog amplifier. It performs phase inversion of analog signals. Further, as a method for inverting the phase of a digital signal, the phase is inverted by inverting a 16-pit PCM signal from a digital signal processing device.

Figure 2(a) is a block diagram of the latter case, where 1 is a digital signal processing device, 2 is a phase inversion circuit (there is a circuit for 16 bits), 3 is an integral type DA converter, and 4 is an analog low-pass filter. , AIB is the PCM signal (16
bit), C, Dtj near.

signal, and E is a phase-inverted signal. Also, Figure 2) is a configuration diagram for the former case, where 5 is an analog low-pass filter, 6 and 7 are inverted analog amplifiers, 8 is a phase changeover switch, F and G are analog signals, and H is a phase inversion signal. .

<Problems to be Solved by the Invention> However, the above conventional system has the following problems.

In other words, if phase inversion is performed in an analog system, an inverting amplifier 7 must be added, and in the case of stereo signals, it is difficult to adjust the phase difference between the right channel and left channel using an analog amplifier, and the cost increases. It can also cause

On the other hand, if phase inversion is performed in a digital system, the PC
A circuit for inverting the M digital data is required for 16 bits, which increases the cost.
By inverting the CM digital data, an offset error a of one pit occurs as shown in FIG. 3 (a diagram showing the relationship between digital data and analog signals). Although FIG. 3 shows 4 pits for convenience, the same applies to 16 bits. FIG. 5(a) is a diagram before phase inversion, and FIG. 3(b) is a diagram after phase inversion. For CD players, 16 for analog voltages up to 2Vrms.
Quantization is performed using Binoto. Therefore, the voltage value E corresponding to 1 bit is 30.5 μV in 1 bit E1 bit=□6. Therefore, an analog signal with this much error is output as the inverted output signal (see FIG. 4. (a) Figure before two-phase inversion, (b) Figure after two-phase inversion, a: error). Therefore, 1
If the analog signal is inverted by inverting the 6-bit digital data, faithful reproduction of the 16-bit PCM digital data is not possible. Note that in order to eliminate the offset error caused by inverting the 16-bit PCM digital data, it is sufficient to add -1" to LsB, but this increases the hardware and is inefficient.

The present invention aims to solve the above-mentioned conventional problems.

Means for Solving Problems> In a pulse density modulation DA converter system, the phase of the analog signal is inverted by inverting the PDM signal, which is the output of the pulse density modulator, using a phase inverting circuit.

<Example> Hereinafter, the present invention will be described in detail based on Examples.

As shown in FIG. 1, the DA converter system 11 according to the present invention includes a pulse density modulation type DA converter 111 having a phase inversion function, and rectifies the output PDM signal Y' of the DA converter 111 into an analog signal Z. It consists of an analog low-pass filter 112 for conversion. The DA converter 111 includes a pulse density modulator 113 that converts the PCM signal
and a phase inversion circuit 114 that selectively outputs the signal to Y'.

First, the pulse density modulator 113 will be explained.

FIG. 5 is an internal circuit configuration diagram of an example of the modulator.

In the figure, 121, 122 and 123 are clocks φ
A delay circuit (D latch) that captures data by
124 and 125 are adders, 126 is a multiplier with a multiplier of 2,
A comparator 127 outputs 0 or 1 depending on whether the result of the operation by the adder 125 is positive or negative. Also, X is 1
6-bit input PCM signal, Y is 1-bit output PDM
In the configuration shown in FIG. 5, the following relationship holds true.

X1S□・z −y−z =s□ ・・・・・・
・・・・・・・・・・・・・・・■S1・Z+S2・Z
-2Y-Z =S2・・・・・・・・・・・・■
Y-82+N ・・・・・・・・・・・・・・・・・・
...... ■In the above formula (■), N is noise generated due to quantization to 1 bit. Also, z-1
indicates the delay due to clock φ.

According to the above formulas ■, ■, ■, Y=X・Z +N(1-Z-1)2 ・・・・・・・・・
・・・・・・・・・・・・・・・・・・In the 00 type,
Although X has a coefficient of z-1, this only causes a delay by the period T of the clock φ and does not affect the noise distribution or frequency characteristics at all.

In other words, the output Y has a delay of T with respect to the input X, but it is completely unrelated to the S/N ratio of the PDM output signal, and
The second term (1-Z'') is expressed as a noise component.

In addition, since the N(1z-1)2 term representing the noise component is close to O in the low frequency region, N(1-Z-')2
Therefore, the equation (■) is SN in the low frequency region.
This shows that the model formula has a very good ratio.

An example of the PDM signal is shown in FIG. By passing this PDM signal through an analog low-pass filter, it is converted into an analog signal Z (see FIG. 7).

Next, the phase inversion circuit 114 will be explained.

As shown in FIG. 8, the phase inversion circuit 114 consists of an exclusive OR circuit 131.

First, the phase inversion signal PI (signal output from a key switch or microcomputer) is at a low level (-〇“).
If so, the PDM signal from the pulse density modulator 113 is supplied to Y' with the signal phase.

Next, the phase inversion signal PI goes to High level (N1")
If so, it becomes the phase of the PDM signal from the pulse density modulator 113 and is supplied to Y'. Then, by rectifying this signal with an analog low-pass filter,
A signal with an opposite phase to the signal output from the digital signal processing device is output as an analog signal (7th
See diagram. Z: Analog signal flowing PDM signal signal).

No offset error occurs even if the PDM signal is phase inverted. This is because there is no power difference when the phase of Y172 in FIG. 9(a) is inverted.

FIGS. 9(a) and 9(b) are diagrams showing the relationship between PDM signals and levels. b is an analog voltage value corresponding to the PDM signal.

<Effects of the Invention> As explained in detail above, according to the present invention, (11P
Since phase inversion is performed on the DM signal, there is no quality deterioration in the analog system after the DA converter, and only the phase difference can be reproduced.
In a digital audio system such as a player or a DAT player, there is no need to do complicated things such as inverting 16V PCM digital data.

f3116biso) A 1-bit offset voltage difference occurs by inverting the PCM digital data, but the PD
Even if the M signal is inverted, no offset voltage difference occurs.

(4) Furthermore, by incorporating a phase inversion circuit into the DA converter, absolute phase can be reproduced, thereby providing high quality digital stereo reproduction sound.

It is possible to obtain an extremely useful A converter system that exhibits the following effects.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a DA converter system according to the present invention. FIGS. 2(a) and 2(b) are block diagrams showing the configuration of the conventional system. Figure 3 is a diagram showing the relationship between digital data and analog signals in the conventional method shown in Figure 2(a), where (a) is before phase inversion, and Figure (b) is after phase inversion. This is a diagram. Figure 4 is a diagram showing the offset error.
) is a diagram before phase inversion, and (b) is a diagram after phase inversion. FIG. 5 is a block diagram showing the configuration of the pulse density modulator. FIG. 6 is a signal waveform diagram showing an example of a PDM signal. FIG. 7 is a diagram showing the relationship between the PCM signal X, the PDM signal Y, Y, and the analog signal Z, Z. FIG. 8 is a configuration diagram of a pulse density modulation type DA converter with a phase inversion function that constitutes the DA converter system according to the present invention. FIGS. 9(a) and 9(b) are diagrams showing the relationship between PDM signals and levels. Explanation of symbols 11: DA converter system, 12: Digital signal processing device, 111: Pulse density modulation type DA converter with phase inversion function, 112: Analog low-pass filter, 113: Pulse density modulator, 114: Phase inversion circuit, P■ : Phase inversion signal 0

Claims (1)

[Claims] 1. In a DA converter system including a pulse density modulator that converts an input PCM signal to a PDM (pulse density modulation) signal, and an analog low-pass filter that converts the PDM signal to an analog signal, A phase inversion circuit is provided between the pulse density modulator and the analog low-pass filter for selectively outputting the output PDM signal of the pulse density modulator or its inverted signal based on the phase inversion signal. D.A.
converter system.