JPH03178223A - D/a converter circuit - Google Patents

Abstract

PURPOSE:To decrease the absolute value of zero cross distortion and to reproduce a minute level signal with fidelity by providing a difference value generating circuit outputting a digital signal being a difference between a current sampling and a preceding sampling and a sample-hold capacitor converting an analog current signal into a voltage signal and outputting the resulting signal to a low pass filter. CONSTITUTION:A difference value generating circuit 3 generating a digital signal representing a difference between a current sampling and a preceding sampling value and outputting the result to a D/A conversion circuit 2 and a sample-hold capacitor 4 converting an analog current signal from the D/A conversion circuit 2 into an analog voltage signal and outputting the converted signal to a low pass filter are provided. The difference value generating circuit 3 is constituted of series connection of an SIPO (serial-in parallel-out) register 31, a PISO (parallel-in serial-out) register 32, a shift register 33, a subtractor 34, another SIPO register 35, and another PISO register 36. Thus, the D/A converter circuit is realized, in which the production of zero cross distortion itself is suppressed and no error compensation processing is required.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a digital/analog conversion circuit (hereinafter also referred to as a D/A conversion circuit) in various digital audio equipment such as a compact disc player (CD player).

) regarding.

<Prior Art> Generally, a D/A conversion circuit in a CD player company of digital audio equipment converts a digital signal of a predetermined number of bits, for example 16 bits, input from a digital signal processing circuit into an analog signal and passes it through a low-pass filter. <Problem to be Solved by the Invention> However, in the conventional ladder resistance type D/A conversion circuit, the error in the resistance greatly affects the accuracy of the D/A conversion circuit. The resistors are set to a controlled precision by laser trimming. However, this error is MSB (th
e Mo5t Stgnificant Bit
), and zero-crossing distortion occurs when the MSB bit is inverted, making it difficult to faithfully reproduce minute-level signals.
The error was compensated for by adding a current or voltage to the circuit output that canceled out the error.

In view of the above-mentioned problems, the main object of the present invention is to provide a D/A conversion circuit that suppresses the occurrence of zero-cross distortion itself and does not require error compensation processing as described above.

Means for Solving the Problem> In order to solve this problem, the digital/analog conversion circuit of the present invention includes a ladder resistance type digital/analog conversion circuit section and a current sampling value indicated by the digital signal of the digital signal processing circuit. A digital signal indicating the difference between the value and the previous sampling value is generated and outputted to the digital/analog conversion circuit section.The analog current signal from the difference value generation circuit and the digital/analog conversion circuit section is converted into an analog voltage signal. It is characterized by comprising a sample and hold capacitor that converts the data and outputs the converted signal to a low-pass filter.

<Example> Embodiments of the present invention will be described below based on the drawings.

Figure 1 shows the configuration of one embodiment of the digital/analog conversion circuit.
FIG. 2 shows a block configuration of a CD player to which this digital/analog conversion circuit is applied.

The D/A conversion circuit 1 includes a D/A conversion circuit section 2, a difference value generation circuit 3 provided before the D/A conversion circuit section 2, and a D/A conversion circuit section 2.
It consists of a sample and hold capacitor 4 arranged after the A conversion circuit section 2.

The difference value generation circuit 3 receives the MS from the digital signal processing circuit 5.
B The current sampling value (for example, 1
6-bit data) and the previous sampling value (16-bit data), and serially D/A this digital signal using MSB FST.
It is output to the conversion circuit section 2. Specifically, the difference value generation circuit 3 includes 5 IPO (serial in/parallel out) registers 31 . PISO (parallel in)
serial out) register 32, shift register 33,
subtractor 34, other 5 IPO registers 35, other prso
This configuration has registers 36 connected in series. here,
S! PO register 31 and PISO register 32 are MSB
A circuit that converts FST to LSB FST, a shift register 33, a subtracter 34 that subtracts the current data and the previous data, 5IPO register 35, PIS
O register 36 subtracts the result from LSB FST to MS
This is a circuit that converts to B FST.

The D/A conversion circuit section 2 is of a well-known ladder resistance type, and converts the difference value digital signal manually inputted from the difference value generation circuit 3 by MSB FST into a positive/negative analog current signal and sends it to the sample hold capacitor 4. Output.

One sample hold capacitor 4 is the D/A conversion circuit section 2
It is charged and discharged by the positive and negative analog current signals inputted from the terminal and outputs an analog voltage signal to the low-pass filter 6. Here, if the analog current signal is Δi, the capacitance of the sample-and-hold capacitor 4 is C1, and the charging voltage is Vc (t), then the charging voltage Vc (t) is Vc (t) = Δ i -t/C+ Vc (Vc :
The charging voltage one clock ago) is given by . As is clear from this equation, it can be seen that the charging pressure Vc(t) changes linearly with respect to time t (see FIG. 3).

In Fig. 2, the reference numeral 7 indicates an optical deck mechanism;
8 represents a digital signal circuit, 9 represents an analog signal circuit, and 10 represents a system control section.

<Operations and Effects of the Invention> As explained above, the digital/analog conversion circuit of the present invention has a ladder resistance type digital/analog conversion circuit section and a current sampling value and a previous sampling value indicated by the digital signal of the digital signal processing circuit. a difference value generation circuit that generates a digital signal indicating a difference value and outputs it to the digital/analog conversion circuit section; and a low-pass filter that converts the analog current signal from the digital/analog conversion circuit section into an analog voltage signal. It is characterized by consisting of a sample and hold capacitor that outputs to.

Therefore, since the required number of bits of the differential value digital signal is small, the absolute value of zero-cross distortion in the D/A conversion circuit section is small, making it possible to faithfully reproduce minute level signals.

Furthermore, since the analog voltage signal changes linearly rather than stepwise, it is possible to omit a low-pass filter at the subsequent stage as necessary.

Note that the present invention is not limited to the above embodiments,
It can be applied even if the input format is parallel or LSBFST. Further, the present invention can be applied to both two's complement and offset binary digital signal formats.

[Brief explanation of drawings]

Figure 1 is a block diagram of an embodiment of the digital/analog conversion circuit of the present invention, Figure 2 is a block diagram of a CD player to which the digital/analog conversion circuit is applied, and Figure 3 is the digital/analog conversion circuit described above. FIG. 2 is an explanatory diagram of an output waveform. DESCRIPTION OF SYMBOLS 1... Digital/analog conversion circuit, 2... Digital/analog conversion circuit section, 3... Difference value generation circuit, 4... Sample hold capacitor, 5... Digital signal processing circuit, 6...・Low pass filter. Patent application Hitoshi Shirasago Electric Co., Ltd. Vc Figure

Claims (1)

[Claims] A ladder resistance type digital/analog conversion circuit unit, which generates a digital signal indicating a difference value between the current sampling value and the previous sampling value indicated by the digital signal of the digital signal processing circuit; A digital audio device comprising: a difference value generation circuit that outputs to a circuit section; and a sample-hold capacitor that converts an analog current signal from the digital/analog conversion circuit section into an analog voltage signal and outputs it to a low-pass filter. digital/analog conversion circuit.