JPS63246927A - Reference voltage generating circuit - Google Patents

Abstract

PURPOSE:To decrease the chip area by providing a 1st switch circuit connecting to a resistor connected to a DC power supply and to each division node of a 1st division resistance string and a 2nd switch circuit connecting a resistor connected to ground and each division node of a 3rd division resistance string. CONSTITUTION:A DC power supply VCC is connected to a resistor R0 whose resistance is R/2, the resistor R0 is connected to division points a1-a4 of a 1st resistor string comprising resistors R1-R3 whose resistance is R via changeover switches 2-1-2-4 of the switch circuit 2. On the other hand, the earth point is connected to a resistor R10 whose resistance is R/2 and the resistor R10 is connected to division points a7-a10 of a 3rd resistor string comprising resistors R7-R9 whose resistance is R. Thus, number of connections with a selector 1 corresponding to the reference division resistor is reduced remarkably and the chip area is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a reference voltage generation circuit, and more particularly to an improvement in a standard voltage generation circuit that generates a reference voltage using divided resistors.

[Conventional technology]

Generally, when determining the level of an analog voltage and converting it into a digital value in an A/D converter, etc., a plurality of divided resistors are used as means for generating a reference voltage for comparing and checking the level of the analog voltage. A reference voltage generation circuit is used.

Conventionally, in this type of reference voltage generation circuit, as shown in the block diagram of FIG.
c and ground open sound, R/2 [Ω] resistance and 15 R [Ω]
) and a resistor of R/2 [Ω] are connected in series, and the DC power supply Vcc is connected to the dividing point b+ to L) 16
It is divided into 16 parts via f. The voltages corresponding to the division points b+ to b4 are sent to the selector 5&, and the voltages corresponding to the division points b9 to b+z are sent to the selector -7, and the voltages corresponding to the division points b! Voltages corresponding to s to b1a are input to selectors 8, respectively.

The conventional example shown in the third tA is a configuration example of a reference voltage generation circuit when the resolution is 4 bits.
, 7j? and 8, the select signal S
2 and Sl are input to 2, and this select signal controls 1llJ, and selectors 5, 6, 7 and 8 select dividing points b+~b< and dividing points b5~b8, respectively.
, dividing points b9-blz and dividing points L++5-Lz6
A voltage corresponding to one division point selected at each V is selected from among them and outputted from the selector 4 VC.

Selector 4 selects select signals So and S from among the four divided voltages that can be manually controlled by selectors 5, 6, and 7.8.
One voltage is selected from IK and output as the reference voltage Vref. That is, the select signals So, Sl, 8
2, Ss, and S4 can generate 16 types of reference voltages.

[Problem that the invention seeks to solve]

The above-mentioned conventional reference voltage generation circuit is connected to a type-1 reference voltage array for generating divided resistors with equal resistance values, and selects one of the division points of each divided resistor including both ends. Since the configuration is such that when the resolution of the reference voltage is increased, the number of dividing points corresponding to the dividing resistors will increase, and therefore one of the dividing points will be selected and output as a reference voltage. The configuration of the selector that selects and outputs the dividing point is also complicated, and when these are implemented using an integrated circuit, the chip area increases.

For example, when applying the conventional example shown in FIG. 3 to an 8-bit resolution reference voltage generation circuit, two R/
2 (Ω) resistance [(7Mlt1255 (=2a-1)
Since one of the 256 dividing points of the dividing resistor must be selected and output, there is a large number of wiring from each dividing point to the selector.Also, control using an 8-bit select signal requires less manual effort. The configuration of the selector to be selected also becomes complex. For example, when implementing a one-chip micro combinator that incorporates an A/D converter along with various peripheral circuits, the area of the reference voltage generation circuit is smaller than that of other peripheral circuits. is large, which is a factor in increasing the area of the entire chip.

[Means for solving problems]

The reference voltage generation circuit of the present invention is a reference voltage generation circuit that generates a reference voltage by connecting a dividing resistor between a DC power source and the ground. 1 divided resistor string, a second divided resistor string in which (n-1) resistors of nR (Ω) are connected in series, and a third divided resistor string in which n resistors of R [Ω] are connected in series. A series of resistor strings are connected in series in the order of the first, second, and third divided resistor strings to form the reference divided resistor string, and the R/2[Ω A first switch circuit that independently selects and connects the resistor of ] and each divided contact of the first divided resistor string;
2 [Ω] resistor and the third divided resistor string); and a selector that selects one of the divided contacts and outputs a reference voltage.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. This embodiment is an example of generating a reference voltage with 4-bit resolution, and includes a selector 1, switch circuits 2 and 3, and nine resistors R1 to R.
9, and resistors Ro and Rho having a resistance value R/2 [Ω].

In FIG. 1, the switch circuit 2 has a select signal (S
l, 52) Changeover switch 2-1 ~ controlled by K
2-4, the switch circuit 3 includes a changeover switch 3 whose switching is controlled by a select signal (Sl, S2).
-1 to 3-4 are included. The DC power supply Vcc is R/
2 [Ω] resistor RO, and the resistor RO is connected to each selector switch 2-1, 2-2, 2-3, 2 of the switch circuit 2.
-4, each resistor R1, R2, R with a resistance value R [Ω]
3) Each dividing point a1.
a2. a3. formed to be connected to a4, while
The ground point is connected to a resistor Rro of R/2 [Ω], and the resistor Rto is connected to the switch circuits 3-1, 3-2, 3-3,
3-4, each resistor Rr, Rs with a resistance value R [Ω]
, Rs) at each dividing point a7. all, a9. al.

It is formed to be connected to. Further, between the first and third resistor strings, there is a second resistor string consisting of resistors R4, Rs, and Re each having a resistance value of 4R (Ω).
J-rings are connected in series, and each dividing point a4, a5.

a6. a7 are each connected to selector 1.

When the select signal (Sl, 52) = (0°0) is input to the naitch circuit 2, the changeover switch 2-1 of the switch circuit 2 is turned on, the changeover switch 2-2% 2-4 is turned off, In the switch circuit 3, the changeover switch 3-1 is turned on, and the changeover switches 3-2 to 3-4 are turned off. At this time, the select signal (Sl.

So), as shown in Figure 2 (1), (IZ5/16)Vcc and (8,5/16)Vc, respectively.
c, (4,5/16)Vcc, (0,5/16)Vcc
Four types of reference voltages Vref can be obtained. In addition, in FIG. 2 (1), (21, (31, (41), the resistance values R[
Ω] is listed, and a resistance value of 4R [Ω] is listed for each of the resistors 1ζ4 to RaK.

Next, when the select signal (S5, 52) = (0, 1), the changeover switch 2-2 of the switch circuit 2 is turned on, the changeover switches 2-1, 2-3, and 2-4 are turned off, and the switch circuit The changeover switch 3-2 of No. 3 is turned on, and the changeover switches 3-1, 3-3, and 3-4 are turned off. At this time, depending on the combination of select signals (Sl, So),
1C show f! : ') VC(13,5/16)Vc
c.

(9,5/16)Vcc, (5,5/16)Vcc, (
1, 5/16) Vcc, four types of reference voltages Vref can be obtained. Similarly, select signal (S:l, 52)=
(1,0) and'a VCu2 shown in Figure t31 f
YoK (14,5/16)Vcc.

(10,5/16)Vcc, (6,5/16)Vcc,
(Z5/16)Vcc 4 types of reference voltage Vref
is obtained, and when the select signal (83, 52) = (1, 1), as shown in Fig. 2 (41), '5IC (15, 5
/16)Vcc, (11,5/16)Vcc, (7,5
/16)Vcc, (3,5/16)Vcc 04 reference voltages Vref can be obtained. Therefore, a total of 16 reference voltages can be obtained by combining the select signals (Sl, S2) & (St, So).

In the above embodiment, the case of 4-bit resolution was explained, but it is generally applied also to the case of N (positive integer) bit resolution. For example, in the case of 8-bit resolution, the resistance value shown in Fig. 1 is applied. Resistance Ro of R/2 [Ω] and Rlo
Among the resistor strings connected in series between the two, the first resistor string and the third resistor string each have a
The IJ ring is composed of 5 R[Ω] resistors, and the third resistor is composed of 15 16R[Ω] resistors. In this case Id, (0,5/256)V
256 reference voltages from cc to (255,5/256)Vcc are obtained.

In each of the cases of 4-bit resolution and 8-bit resolution described above, the number of connections between the two switch circuits and the corresponding resistor strings is 8 in total in the former case, and 32 in total in the latter case. Resistance corresponding to selector) I
The number of connections to the J-ring is 4 in the former case and 16 in the latter case.

The number of these connections is significantly reduced compared to the number of connections in a conventional reference voltage generation circuit. In particular, the reduction in the number of connections becomes more pronounced as the resolution increases.

Although the switch circuits shown in FIGS. 1 and 3 are mechanical switches, it is possible that the reference voltage generation circuit of this embodiment can be constructed using MOS transistors or the like when implemented on an integrated circuit. Needless to say.

〔Effect of the invention〕

As explained above, the present invention can be applied to a reference voltage generation circuit configured by connecting a reference dividing resistor between a DC power source and the ground, and the voltage between the reference dividing resistor and a corresponding selector, etc. By significantly reducing the number of connections,
It is possible to simplify the configuration of the selector, etc., and implementation using an integrated circuit is also possible with an extremely small chip area.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a reference voltage generation diagram in the embodiment, and FIG. 3 is a block diagram of a conventional reference voltage generation circuit. 1.4.5.6.7.8...Selector, 2゜3...Switch circuit, 2-1 to 2-4.3-1
~3-4......Selector switch. Agent Patent Attorney Uchihara n.
,−'. , ) Vcc Reed 1 ■ Vc Vcc VCCVctCf)
27

Claims (1)

[Claims] In a reference voltage generation circuit that generates a reference voltage by connecting a reference dividing resistor between a DC power source and the ground, a first circuit in which n (positive integer) resistors of R [Ω] are connected in series. A divided resistor string, a second divided resistor string consisting of (n-1) resistors of nR [Ω] connected in series, and a resistor of R [Ω] connected in series.
a series of resistor strings formed as the reference divided resistor by connecting the first, second and third divided resistor strings in series in the order of the first, second and third divided resistor strings connected in series; R/2 connected to
a first switch circuit that independently selects and connects a resistor of R/2 [Ω] and each divided contact of the first divided resistor string, and a resistor of R/2 [Ω] connected to ground and the third a second switch circuit that independently selects and connects each divided contact of the divided resistor string; and a second switch circuit that selects one divided contact from among the divided contacts of the second divided resistor string and applies a reference voltage to the divided contact. Selector to output and
A reference voltage generation circuit comprising: