JPS6154717A - Da converter circuit - Google Patents

Abstract

PURPOSE:To attain the simplification of circuit constitution which is conventionally regarded as impossible by setting the output impedance in a constant impedance area where an MOS field-effect transistor (TR) operates in a saturated state to the value of a resistance to be connected in series, and using the field- effect TR as a resistance element in common. CONSTITUTION:Output impedance values of a PMOS FET21A and an NMOS FET 21A which constitute a CMOS FET21 in constant impedance area where they operate in a saturated state are controlled to the resistance value of a resistance element 9. Similarly, output impedance values of PMOS FETs 22A and 24A and NMOS FETs 22B and 24B as elements of CMOS FETs 22 and 24 in constant impedance areas where they operate in a saturated state are set to resistance values of resistance elements 10 and 12. Thus, MOS field-effect TRs are used as resistance elements, so the number of circuit elements is decreased by the number of the resistance elements.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a DA converter circuit using a MOSg field effect transistor as a switching element, and particularly to a DA converter circuit having a resistance element connected in series to the switching element. .

[Background of the invention]

Conventionally, in a DA converter circuit of the type shown in Fig. 1, in which several circuits are constructed of a switch and a resistor network, the switch is composed of a switching element, the resistor network is composed of a resistor element, and the circuit configuration is as follows. It was thought that there was no way to simplify it any further. Note that Fig. 1 shows an R-2B ladder one-resistance type DA converter circuit with a 0MOS field effect transistor (FET) as a switching element.
0 MOSFETs in which ~4 consists of PM03 F'ETIA~4A and NMO5FETI B~4B, respectively;
5 to 1 are resistance elements with a resistance value of 2R, 8 to 12 are resistance elements with a resistance value of 2R, and a 4-bit digital signal from the most significant bit to the least significant bit is input to terminals 13 to 16, and corresponding from terminal 11. An analog output is obtained. Also V
REF is the power supply, which is pressure.

[Purpose of the invention]

The present invention addresses such circumstances as VC! The purpose of this invention is to provide a DA converter circuit whose circuit configuration has been simplified, which was thought to be impossible in the past.

[Summary of the invention]

In order to achieve such an object, the present invention makes the output impedance in a constant impedance region equal to the value of the resistor to be series connected thereto when the MOSfi field effect transistor constituting the switching element operates in a saturated state. In particular, the MOS field effect transistor is also used as a resistance element.

[Embodiments of the invention]

FIG. 2 is a circuit diagram showing an embodiment of the present invention when applied to a circuit having the same function as the conventional circuit shown in FIG.

As is clear from comparing both figures, in this embodiment, only the 0MOSFETs 21 to 24 are connected to the input section of each digital signal, and the resistive elements 9 to 12 connected in series to the 0MOSFETs 1 to 4 in FIG. are not connected as independent circuit elements. Instead, in this example,
During the manufacturing process of 0MOSFET21, this 0MOS
The output impedance in a constant impedance region where FET1 to PMOSFB'l'21A constituting the transistor operate in a saturated state and the similar output impedance of NMOSFET21B are controlled so as to be equal to the resistance value of resistance element 9. Similarly, the output impedance of the 0MOSFETs 22 to 24 in a constant impedance region in which they operate in the saturated state of the component PM08 FETs 22A to 24A and NMOSFETs 22B to 24B is set equal to the resistance value of the resistance elements 10 to 12, respectively,
This results in independent resistance elements 9 to 12? I
The same effect as when connected in series is obtained.

The above description has been made with reference to the case where the present invention is applied to a 4-bit ladder single-resistance type DC converter circuit, but the present invention is not limited to this, and is applicable to circuits with different bit numbers and weighted-resistance type DA converters. Needless to say, the present invention can be similarly applied to converter circuits and the like.

〔Effect of the invention〕

As explained above, according to the present invention, when the MOS field effect transistor constituting the switching element operates in a saturated state, the output impedance in the constant impedance region is made equal to the value of the resistor to be connected in series.
By also serving as a SiO8 field effect transistor element, the number of circuit elements can be reduced by the number of resistor elements that can be replaced with a MOS [field effect transistor], and the circuit configuration can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of the configuration of a conventional DC converter circuit, and FIG. 2 is a circuit diagram showing an embodiment of the present invention.

Claims (1)

[Claims] A resistor to which the output impedance in a constant impedance region where the MOS field effect transistor operates in a saturated state is connected in series in a DA converter circuit including a switching element consisting of a MOS field effect transistor and a resistance element connected in series to the switching element. A DA converter circuit characterized in that the MOS field effect transistor is set equal to the value of , and the MOS field effect transistor is also used as a resistance element.