JPH01132221A - Da converting circuit - Google Patents

Abstract

PURPOSE:To widely shorten a convertion time by separating an input digital signal into a high-order bit and a low-order bit, DA-converting one of them by a resistive dividing type converting part, DA-converting the other by an integration type converting part, adding the outputs of the two converting parts and obtaining an output analog signal. CONSTITUTION:A first converting part 21 is the resistive dividing type converting part composed of resistors 22-25 connected in series between a power source +Vr1 and an earth and switches 26-29 whose one ends are connected with the connection midpoints of the resistors 22-25. When the input digital signal is 4-bit, the digital signal of high-order 2 bits is selected by a first selecting circuit 17, latched by a latch circuit 19 and impressed on a decoder 20. The digital signal of low-order 2 bits is selected by a second selecting circuit 18 and latched by a latch circuit 2 of an integration type second converting part 30. The decoder 20 decodes the digital signal of the high-order 2 bits and generates a control signal to open-close-control the switches 26-29. An adding circuit 31 adds the outputs of the two converting parts. A converting speed is determined by integration time to the digital signal of the low-order bits and it is widely shortened comparing with a conventional case.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a DA conversion circuit for converting a digital signal to an analog signal, and more particularly to a DA conversion circuit that can significantly reduce conversion speed.

(b) Conventional technology A published by Ohmsha on September 25, 1980
/D Converter Introduction” pages 162 and 163,
An integral type DA conversion circuit has been presented.

The above-mentioned integral type DA conversion circuit is currently used in the field of digital audio and the like because it has excellent linearity and monotonicity. Figure 2 shows such an integral type DA converter circuit, in which the input digital signal applied to the input terminal (1) is latched by the latch circuit (2) and sent to the digital comparator circuit (3).
) is applied to

The digital comparison circuit (3) also includes a counter (4).
) is applied to the counter (4), and the counting operation of the counter (4) is controlled by a control circuit (5). The conversion unit that converts a digital signal into an analog signal includes an amplifier circuit (6), first and second switches (7)
and (8), an integrating circuit (11) consisting of a capacitor (9) and a resistor (lO), and a sample hold circuit (12) that samples and holds the output signal of the integrating circuit (11).
The first and second switches (7) are controlled by a control signal generated from the control circuit (5).
Integral operation is performed by controlling the opening and closing of (8) and (8).

When performing DA conversion using the DA conversion circuit shown in Fig. 2,
First, a first control signal Sl is generated from the control circuit (5),
Close the first switch (7) and discharge the capacitor (10). Thereafter, the first control signal S1 is stopped and the second control signal S is generated from the control circuit (5), the second switch (8) is closed, and the integration operation is started. At the same time, the counting operation of the counter (4) is started. The counting operation of the counter (4) is performed by a latch circuit (2).
The value of the output signal of > matches the count value of the counter (4), and a match signal is generated from the digital comparator circuit (3). When the coincidence signal is generated, the control circuit (5)
The second control signal S, from the second switch 8) is stopped.
is opened and the integral operation stops. The output signal of the integrating circuit (11) is then sampled and held in a sample and hold circuit (12), and an output analog signal corresponding to the input digital signal is generated at the output terminal (13).

If the reference voltage applied to the reference terminal (14) is shifted from -Vr, the current (2) flowing through the resistor (9) will be as follows: [where R is the resistance value of the resistor (9)]. Further, the capacitor (10) is connected to the resistor (9).
Since the current flowing through the capacitor (10) is charged with a constant current of 1, the voltage Vc across the capacitor (10) is: ■ Vc=-t ・・・・・・・・・・・・
...(2). In that case, the clock terminal (1
5) If the count value of the counter (4) until the T1 coincidence signal is generated is n, then from the above equations (1) and (3), the following equation is obtained. Therefore, by using the DA conversion circuit shown in Fig. 2, it is possible to convert the input digital signal (corresponding to n above) into an analog signal (corresponding to vc above), and if this analog signal is sampled and held, the output terminal ( 13) An output analog signal can be obtained.

(c) Problems to be solved by the invention However, the integral type DA conversion circuit as shown in FIG.
Since the integration time increases in accordance with the number of bits of the input digital signal, there is a problem that the maximum value (HMA!) of the number of clocks to be counted increases as the bits become higher, and the conversion time becomes extremely long. For example, when performing N-bit conversion, the nM□ becomes 2N-1, if N = 8, nMAx = 255, and if N = 16, nvAx
= 65535, so it cannot actually be used as a high-order bit DA conversion circuit.

(d) Means for solving the problems The present invention has been made in view of the above points, and includes means for separating an input digital signal into upper bits and lower bits;
a decoder that decodes a digital signal of one of the separated upper bits and lower bits; a first conversion section that includes a plurality of resistors and switches connected in series and generates an analog signal according to the output of the decoder; A second conversion section that integrates the other digital signal of the upper bits and lower bits to generate an analog signal, and an addition circuit that adds the output analog signals of the first and second conversion sections. shall be.

(f) Effect According to the present invention, an input digital signal is separated into upper bits and lower bits, one of which is subjected to DA conversion in the first converter of resistance division type, and the other is converted to analogue by the second converter of integral type. Since the output analog signal is obtained by adding the output signals of the two-way converter, the conversion time can be significantly shortened, and a highly accurate DA conversion circuit can be provided.

(f) Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention, (16)
is an input terminal to which an input digital signal is applied; (17) is a first selection circuit that operates as a separation means for selecting the upper bits of the digital signal; and (18) is a separation means for selecting the lower bits of the digital signal. The operating second selection circuit (19) is a latch circuit that latches the output signal of the first selection circuit (17), and (20) is the latch circuit (20).
A decoder (4,) decodes the output signal of 19), which includes first to fourth resistors (22) to (25) connected in series between the power supply (+Vr+) and the ground, and one end of which is connected to the first to fourth resistors (22) to (25). A first converting section (former) consisting of first to fourth switches (26) to (29) connected to the connection midpoints of resistors (22) to (25) is connected to the second selection circuit (18). (31) is an addition circuit that adds the output signals of the first and second converters (fu) and (hidden); and (32) is an output analog signal. This is the output terminal that provides the output. In addition, the integral type second conversion section (sub)
The structure and operation are the same as those of the DA conversion circuit of FIG. 2, and the same reference numerals are given, and the explanation will be omitted.

Now, if the input digital signal is 4 bits, the upper 2 bits of the digital signal are selected by the first selection circuit (17), latched by the latch circuit (19), and sent to the decoder (20).
is applied to Further, the lower two bits of the digital signal are selected by the second selection circuit (18) and latched by the latch circuit (2) of the second converting section.

The decoder (20) decodes the upper 2 bits of the digital signal and decodes the first to fourth switches (26) to (2).
9) Generate first to fourth control signals for controlling opening/closing. In other words, 2-bit digital signals "00", '01
J% '10J% '11' as four types of first to fourth control signals' o o 01 J, '0010', '0
100J, rlooo".

For example, when the 2-bit digital signal is 110'', the third control signal '0100J is generated and the second switch (27
) to close. First to fourth resistors (22) to (25)
If the values of .

Further, the output voltage V of the integral type second conversion section (east) is Vr according to the above equation (4).

V, =-・nT ・・・・・・・・・・・・
(6) CR [However, -Vrt is the reference voltage applied to the reference terminal (14)]. The addition circuit (31) adds the voltages V and V. Therefore, the output analog voltage v0 generated at the output terminal (32) is 1. =v, +v, =blood+blood, n001010066. (
7) Becomes CR. If the relationship between the power supply voltage Vr+ and the reference voltage -Vrt is appropriately set, the output analog voltage V.

corresponds to the input digital signal, and DA conversion is achieved.

In the case of the DA conversion circuit shown in FIG. 1, the conversion speed is determined by the integration time for the digital signal of the lower bits, and is significantly reduced compared to the conventional case. For example, when converting a 4-bit digital signal from digital to analog, the circuit in Figure 2 takes a maximum of 15 (=2N-1) clocks, but the circuit in Figure 1 requires a maximum of 3 clocks. DA conversion can be performed in a time equivalent to (=2"-1) clocks.The effect of reducing conversion time increases as the number of bits of the input digital signal increases. For example, in the case of a 16-bit digital signal, the maximum It used to take 65,535 clocks, but now it is 2
The time can be reduced to 55 clocks.

In the embodiment shown in FIG. 1, the DA conversion of the upper bits is performed by a resistor division type, and the DA conversion of the lower bits is performed by an integral type, so that it is possible to shorten the conversion time and improve the conversion accuracy. . However, the present invention is not limited thereto, and conversely, the upper bits may be converted into an integral type, and the lower bits may be converted into a resistor using a resistance division type.

(G) Effects of the Invention As described above, according to the present invention, it is possible to provide a DA conversion circuit that can significantly shorten conversion time. The DA conversion circuit according to the present invention is particularly suitable when a multi-bit DA conversion circuit is required, such as in the field of digital audio.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional DA conversion circuit. <16)...Input terminal, (17), (18)...
・Selection circuit (separation means), (20)...decoder,
(c)...first conversion section, (east)...second conversion section, (31)...addition circuit, (32)...output terminal.

Claims (1)

[Claims] (1) means for separating an input digital signal into upper bits and lower bits, and a decoder for decoding one of the separated digital signals of the upper bits and lower bits;
A resistor-divided type consisting of a plurality of resistors connected in series and a switch whose one end is connected to the connection point of the resistors and whose opening/closing is controlled by the output signal of the decoder, and which generates an analog voltage according to the one digital signal. a first conversion section;
an integral type second conversion section that integrates the other separated digital signal of the upper bit and the lower bit and generates a corresponding analog voltage; and an addition that adds the output analog signals of the first and second conversion sections. A DA conversion circuit consisting of a circuit.