JPS58196722A - Da converter - Google Patents

Abstract

PURPOSE:To average variance in resistance value and to obtain a high-precision conversion output, by comparing a section of a ladder network with variation in input digital value and replacing it at a sufficiently high speed. CONSTITUTION:The ladder network connected annularly is disconnected by one of disconnection switches S9-S16 to constitute a current-mode ladder network D/A converter at this time. The disconnection switches S9-S16 which turn off shift successively, so the ladder network also rotates starting at one section L1 up to a section L8 successively and a weight current is also switched successively. Changeover switches S25 and S32 corresponding to an input digital value are also switched successively and synchronously. Then, the output of an output terminal 18 is averaged by a smoothing circuit 26 to average an analog output due to variance in resistance between the sections L1-L8. Further, this process is applicable to a voltage ladder network type D/A converter.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a DAffi converter that converts a digital cage into an analog value using a resistance ladder network, and is particularly intended to reduce the effects caused by variations in its constituent resistance elements.

[Prior art]

FIG. 1 shows a current mode type DA switching device using a conventional ladder network. Series resistor 11 and shunt resistor 1
A fern network 13 is provided in which sections LIL and Ln are connected in series, one end of the network 13 is connected to a constant current source 14, and the other end is connected to the constant current source 14 through a resistor 15. It is connected to the common potential point at the other end. Each section L of Lada network 13
The other ends of the shunt resistors 120 1 to Ln are connected to the wJ contacts of the changeover switches 81 to Sn, respectively. One fixed contact of each of the changeover switches 81 to Sn is connected to a common potential point, and the other fixed contact of each of the changeover switches 81 to Sn is connected to the inverting input side of the operational amplifier 160. Ribbed. A feedback resistor 17 is connected to the output side of the operational amplifier 16 and its inverted input, and the operational amplifier port 1
The non-inverting input side of 6 is connected to a common potential point.

2 series resistors 11 and 15 of the network 13
, 17, each resistance value is R, ? The resistance value of each shunt resistor 12 of the Dunnett network 13 is set to 2R. The changeover switches Ss to Sn are controlled by each corresponding bit of the binary input digital value, and when the bit is @0'', it is connected to the common potential point, and when it is '1'', it is connected to the inverting input side of the operational amplifier 16. MS (most significant bit of n-bit input digital value)
B selector switch S1 selects the lower bit LSBK.
The changeover switch Sn is controlled. Section L1~
Current 11~in+ flowing through each shunt resistor 12 of Ln
! It is binary weighted. In this case, high n
It is necessary to make each resistance value of the KFi resistors 11 and 120 highly accurate to obtain a conversion accuracy of 1 degree.

[Summary of the invention]

An object of the present invention is to provide a DA converter that can average out variations in resistance values and obtain highly accurate conversion outputs by replacing sections of a ladder network at a sufficiently high speed compared to changes in input digital values. There is a particular thing.

According to an example of the invention, N sections including series resistors and shunt resistors are sequentially connected in a ring shape through disconnection switches, and a shorting switch is connected in parallel with the series resistor of each section. , a movable contact of a changeover switch is connected to the other end of each shunt resistor, one fixed contact of these movable contacts is connected to a common potential point, and the other fixed contact is connected to a common output terminal in the case of a current mode type. In the case of voltage mode type, it is connected to a common power supply. Further, the connection point of each section is connected to a constant current source through a power supply switch in the case of a current mode type, and connected to a common output terminal through an output switch in the case of a voltage mode type.

One of the disconnection switches is turned off, and a power supply switch (or output switch) connected to one side of that disconnection switch
is turned on and connected to the common potential point of the changeover switch connected to the other side, and the i! of the side whose changeover switch is connected to the common potential point! The shorting switch of the I-contacting section is turned on. Further, corresponding to each bit of the input digital value, each changeover switch is connected to one of the changeover switches. The setting state of each switch is maintained by maintaining the relative position on the ring of the section, and sequentially turning off the disconnection switch at a constant interval, and controlling the other switches by the switch control section. By this switch control, the positions of the sections are sequentially changed, and variations among the sections are averaged out.

[First Embodiment] FIG. 2 shows an example in which the present invention is applied to a current keyed type, in which 1108 resistors with a resistance value R are connected to disconnection switches S.
One end of the resistor 12 having a resistance value of 2R is connected to one connection point of each disconnection switch and one of the resistors 11 to form one resistor. A two-way network is constructed in which sections L1 to L- of the vessels 11 and 12 are connected in a ring shape. One short-circuiting switch 81 to S14 is connected to each resistor 11 in parallel. Resistor 1 at the connection point of each section
1 and the connection point of the disconnection switch is the power supply switch 8.
1 to Ss are connected to the constant current source 14. The other end of each resistor 12 is connected to each movable contact of the changeover switches 8as to Ssm, one fixed contact of each changeover switch 3mm to Smm is connected to a common potential point, and the other fixed contact of each of the changeover switches 8as to Ssm is connected to a common potential point. 18.

One disconnection switch Ss@ is turned off, the power supply switch S1 at one end of the disconnection switch S that has been turned off is turned on, and the changeover switch Sag at the other end is connected to a common potential point. # of the side that connects the disconnection switch S, which was turned off, to the common potential point.
The short circuit switch Sss is turned on. When one disconnection switch Sx@ is turned off, a ladder network consisting of cascade connections of one section L1 to Lma is configured, the lower section L1 is connected to the power supply 14, and the section Lma at the other end is connected to the resistor. The resistor 11 is short-circuited by the short-circuit switch Sm5K, and the resistance value R in the resistor 12 of section Lm
and resistor 12 of section Ls constitute one section as a Shirada network, and section Ls
is terminated with a resistor f*R in resistor 12.

When one disconnection switch SS@ is off, the power supply 141i1. of the ladder network is turned off. Section L1
The changeover switch Bam of the input digital value is controlled by the most significant bit of the input digital value, and the changeover switch Sal of the last sexy stage L is controlled by the least significant bit of the input digital value. Similarly, each changeover switch Sag to Sso of sections Lm to Ll is set according to each corresponding bit of the input digital value.
is controlled. For example, if the input digital value is 101000, selector switch 811. The Sl master is on the output terminal 10 side. As the disconnection switches to be turned off are sequentially switched, as the seven-section ladder network is sequentially equipped, the output terminal side of each changeover switch also maintains its relative position with respect to the disconnection switch on the ring. Similarly, the changeover switch that is placed on the common potential point side of the power supply switch that is turned on is also changed while maintaining its relative position with respect to the disconnection switch that is turned off. Third
The figure shows an example of the switch control time chart in FIG. 2 for the case where the input digital value is 101,000.

[Switch control section]

FIG. 4 shows an example of a switch control section that controls the switches in this manner. The control section includes a constant control section 21 that controls the switches 81 to Sl■, and changeover switches Sss to Ss! For example, the constant control section 21 is connected to the output side @@22 that controls the
Flip-flops FFr to FFa are connected in cascade, and the Q output of the final stage 7-lip-flop 1FFs is fed back to the data terminal of the first-stage flip-flop FFI, and the preset data terminal AK of the first-stage 7 lip-flop FFs is set to a high level "1". ” or other flip-flop FF
A low level "θ" is given to the preset data terminal A of 5-FFa, and the flip-flop FF5=FF
The clock terminal of the hatch is a mm-type shift register that performs a shift operation every time a clock is applied from the terminal 23. #43 As shown in Figure A, a load command is sent to the load terminal 24 at time t1 to the flip-flops FF1 to FF1. When applied to each reset terminal P of FFm, @11 and '0' are preset to the flip-flop FFs, and this data pattern @100...O'' is applied to the terminal 23 shown in FIG. 3B.
Shift every clock, flip-flop FFs~
Each Q output Q s to Q port of FFs is shown in Fig. 3 C to J, respectively.
Changes as shown in .

The period of this clock is tiT, and the flip-flop 1
4'F1 to F'F4 Q outputs Q1 to Q8 outputs respectively to power supply switches 81 to 3a and s 1 @ in FIG.
S l 4 *S1 ma~S■ are controlled, and each i output stone 1~Qa of flip-flops FFI~FFa goes up to the third
Disconnection switch 816 in the figure. S- to S-th, changeover switch 3ms, gas to Ss1 are controlled respectively. Control over the switching switches S's to Sms is performed by outputting an AND with the corresponding control signal from the output control section 22, and the output terminal 18@ is at a high level, and the common potential point side is at a low level. Ru.

Similarly to the constant control section 21, the output control section 22 also constitutes a circular shift register by cascading D-type 7 lip-flops FF to FFs. synchronization is achieved. terminal 2
The load command from 4 is the flip-flop FF--FFI.
It is also given to the preset terminal P of
Each bit data of the input digital value stored therein, for example @10100000'', is transferred to a flip-flop FF.
Preset to FFI@. flip flop FFs
- Each Q output of FF1 (-R in FIG. 3) and constant control section 21
The respective outputs to control the changeover switches Sm~S@g are logically ANDed by AND[i1!1ji311~l*, and the changeover switches SSS~Sas are controlled, respectively.

The lug network connected in a ring shape as described above is disconnected at one point by a disconnection switch, a current mode ladder network DA converter is configured at that time, its analog output is output, and the disconnection switch is turned off. As the fern network moves sequentially, the fern network also moves sequentially.
Make one movement for each section. Therefore, the weight current obtained from each section is also sequentially switched. By averaging the output of the output terminal 18 by the smoothing circuit 26, variations between each section are averaged out. Each section consists of a series resistor 11 and a shunt resistor 12, and since there are variations between them, at least one of all the resistors in the fern network has a resistor accuracy of 1'. If the value is adjusted, there is no need to adjust the resistance values of many other resistors 11 and 12 with high precision. Resistor 11.12
Even if there is variation in Because it requires precision,
The resistors 11 and 12 can be incorporated into the semiconductor integrated circuit, and the DA converter can be configured as a semiconductor integrated circuit. Analog switches made of field effect transistors such as disconnection switches, power supply switches, and changeover switches can be used.

[Second Embodiment] In the example shown in FIG.
Each weight current is influenced by the on-resistance of other switches. In order to eliminate this shadow, for example, as shown in FIG. 5 with the same reference numerals attached to the parts corresponding to those in FIG. One emitter of the transistor Trs-Tr- is connected to each of the transistors Trs-Tr-, and the collector of the transistor is connected to each movable contact of the selector switch 8i1-8a. A constant voltage is applied from the power supply 27 to each pace of the transistors Trs-Trs. Therefore, a constant current flows through each of the transistors Trs to Tr, the weight of which depends on the connection state of the resistor connected to the emitter side at that time. For example, in FIG. 5, the power supply switch S1 is on, the changeover switch gH is connected to the common potential point, and the disconnection switch S
In the on state, one half of the constant current flowing through the transistor Trl sequentially flows through the transistors Trm to Tr@. The input digital value is 01 in the octopus diagram.
In the case of 00000, the changeover switch S layer - is the output terminal 18
side, the changeover switch 8mm, 8*ma~8ms is set to the common potential point side.

[Third Embodiment] Although the invention is applied to a current mode ladder network type DA converter in FIG. In FIG. 6, parts corresponding to those in FIG.
2 and the common output terminal 18. In addition, the end of each shunt resistor 12 opposite to the resistor 11 is connected to the movable contact of the changeover switch S. 28. When one disconnection switch, for example S-, is off, the output switch 818 on one side is on, the changeover switch Sss on the other side is connected to the common potential point, and the first stage L MA O of the ladder network at that time is short-circuited. The switches Smm are turned on at the same time, and the disconnection switches S.about.51-1 output switches Sss.about.S4., the changeover switches Sm., and the short-circuit switches S1.about.S. The changeover switches 8 mm to 43 mm are controlled by the output control section 22 according to the corresponding bits of the input digital value, and when the input bit is "1m", the corresponding changeover switches are connected to the power supply 28 side.

When the digital cable connected to output terminal 18 is input, '
.

corresponds to the most significant bit of the total value. In the example shown in Fig. 6, when "1010000-" is input and the disconnection switch S- is off, the selector switch 13m5
．． S 禦v is connected to the power line 0128.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional 0DAi converter, Fig. 2 is a circuit diagram showing an example in which the present invention is applied to a current mode DA converter, and Fig. 3 is a circuit diagram showing control signals for each switch in Fig. 2. A time chart showing an example, Fig. 4 is a circuit diagram showing an example of a switch control section, Fig. 5 is a circuit diagram showing another example of this invention, and Fig. 6 is an application of this invention to a voltage mode type DA converter. FIG. 3 is a circuit diagram illustrating an example. 11: Resistor with resistance value R, 12: Resistor with resistance value 2R,
14: constant current source, 18: output terminal, 21: constant control section, 2
2: Output control section, 26: Smoothing circuit. Patent applicant: Takeda Riken Kogyo Co., Ltd. Takashi Kusano

Claims (2)

[Claims] (1) A series circuit including a disconnection switch, a first resistance element, and a shorting switch connected in parallel, and a second resistance element having one end connected to one end of the series circuit and having a resistance value twice that of the first resistance element. A resistance element and a high-speed resistor are configured, and N stages (N is an integer of 3 or more) of this section are connected in a ring shape.
The connection point of each of these sections is connected to one end of the power supply through a separate power supply switch, and the movable contact of a changeover switch is connected to the other end of each second resistance element of each section. One fixed contact is connected to a common output terminal, and the other fixed point I is connected to the other end of the power supply to turn off a disconnection switch in one of the sections and turn off the disconnection switch that is turned off. Turn on the power supply switch connected to one end, connect the changeover switch connected to the other end to the power supply side, and turn on the power switch of the Ill connection section on the other end of the disconnection switch that was turned off. Turn on, connect the changeover switches to the power supply side or output @IICWI according to each corresponding bit of the input digital value, and set the setting portions of these switches to the above settings so as to maintain their relative positions on the sex drive ring. D is provided with a switch control unit that repeatedly turns off each disconnection switch at a constant period.
A converter. (2) A series circuit of a disconnection switch, a first resistance element, and a short-circuit switch connected in parallel, and a kite two resistance element having one end connected to one end of the series circuit and having a resistance value twice that of the above resistance element. A section is constructed, and N stages (N is an integer of 3 or more) of this section are connected in a ring shape,
- The connection points of each of these sections are connected to a common output terminal through separate output switches, and the movable contact of a changeover switch is connected to the other end of each second resistance element of each section, and each of these changeover switches One fixed contact of is connected to one end of the common power supply, and the other fixed contact is connected to the other end of said power supply, and when a disconnection switch in one of said sections K is turned off, the disconnection switch that is turned off is The output switch connected to one end of the switch is turned on, the changeover switch connected to the other end is connected to the other end of the power supply, and the section adjacent to the one end of the disconnection switch that is turned off Turn on the short-circuit switch, connect the above changeover switch to one end or the other end of the power supply depending on each corresponding bit of the input digital value, and maintain the setting state of these switches and the relative position on the above section ring. The DA converter is provided with a switch control section that repeatedly turns off each of the disconnection switches at a constant period.