JPH04261224A - A/d converter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Description: [0001] The present invention relates to an A/D converter, and particularly to an A/D converter using a ladder resistor. 2. Description of the Related Art FIG. 2 is a circuit diagram showing a conventional configuration of an n-bit A/D converter using ladder resistors. In FIG. 2, reference numeral 1 is a positive reference voltage input terminal, to which a voltage +VREF is input. 2 is the negative side reference voltage input terminal, and the voltage -VREF
is entered. Between both positive side reference voltage input terminals 1 and 2, a resistor 3 with a resistance value of 1.5R, resistors 4a, 4b...4l, each with a resistance value of R, a resistor 40 and a switch element 41 are connected in series. connected switch element 41
A switch element circuit 4m whose resistance value when turned on is about 0.5R is connected in series. In addition, resistors 4a, 4
There are 2n −2 pieces of b...4l in total, and these and 3 resistors
and the switch element circuit 4m constitute a ladder resistance,
The total number of resistors is 2n. Between each resistor 3, 4a, 4b...4l and the switch element circuit 4m, there are 2n-1 intermediate taps 6a for taking out 2n-1 types of comparison voltages.
, 6b...6m are drawn out, and the comparison circuit block 7
It is connected to the. The comparison circuit block 7 includes a selector that selects any one of the intermediate taps 6a, 6b, . It is made up of. Note that the analog input voltage is input to the comparison circuit block 7 from the analog input terminal 8. Also, comparison circuit block 7
A comparator output 10, which is the comparison result by the comparator, is given to the control block 9, and conversely, a control output 11 for controlling the selector and the comparator is given from the control block 9 to the comparison circuit block 7. There is. The control block 9 is composed of a control circuit for controlling the entire A/D converter, a register for storing A/D conversion results, and the like. From this control block 9 to the above-mentioned switch element 41, a comparison voltage enable/control voltage for on/off control of the switch element 41 is supplied.
A disable control signal 12 is provided. Also,
Reference numeral 13 is for external control of the entire A/D converter. An A/D converter control input/output is applied to the control block 9, and 14 is an A/D conversion output output from the control block 9 to the outside. Conventional n-bit A/
The operation of the D converter is as follows. When the A/D converter enable signal is input to the A/D converter control input/output 13 of the control block 9, the comparison voltage enable/disable control signal 12 output from the control block 9 to the switch element 41 is enabled. state, and the switch element 41 is turned on. Next, the A/D converter control input/output 13
When the A/D conversion start signal is input, a control output 11 is output from the control block 9 to the comparison circuit block 7, and the comparison circuit block 7 compares the input voltage of the analog input terminal 8 with the input voltage of each intermediate tap 6a, 6b...6m. A comparator compares the output voltage with one of the output voltages selected by the control output 11 in the control block 9, and outputs the comparison result to the control block 9 as a comparator output 10. The control block 9 inputs the above-mentioned comparator output 10 and stores it in a register, and controls a selector to select the comparison voltage to be selected next based on it. By using a so-called binary search method that sequentially repeats such control, the n-bit A/D converter compares the A/D conversion results corresponding to the analog input voltage input from the analog input terminal 8 n times. It can be obtained through action. When the A/D conversion is completed, control block 9
The A/D conversion result is output from the A/D conversion output 14 of. [0011] In addition, when A/D conversion is not performed,
When the A/D converter disable signal is input to the A/D converter control input/output 13, the comparison voltage enable/disable control signal 12 output from the control block 9 to the switch element 41 becomes disabled. , the switch element 41 is turned off. Thereby, the current between both reference voltage input terminals 1 and 2 is cut off, and wasteful current consumption can be avoided. [0012] Problem to be solved by the invention: The above-mentioned conventional
In the A/D converter, the current between both reference voltage input terminals 1 and 2 is turned on/off by the switch element 41, so the on-resistance of the switch element 41 needs to be a low value. In this case, it is necessary to provide a large element as the switch element 41, which hinders miniaturization of the device and reduction in manufacturing cost. The present invention has been made in view of these circumstances, and it is an object of the present invention to realize functions equivalent to those of conventional A/D converters with a more compact configuration. [Means for Solving the Problems] The A/D converter of the present invention makes a part of the ladder resistor connected to the reference voltage source through the switch element have a high resistance value, and also sets each intermediate tap to a high resistance value. A bypass is provided so that the output voltage is not affected by the difference in resistance value of the ladder resistors, and this bypass is also provided with a switch element for turning on/off the current of the reference voltage source. [Operation] In the A/D converter of the present invention, a low current flows through the ladder resistor whose resistance value has been increased, and this low current is turned on/off by one switch element, and a high current is passed through the side path. A current flows, and this high current is turned on/off by a switching element provided in the side path, and when both switching elements are turned on, the output voltage of each intermediate tap becomes a specified value. [Embodiments] The present invention will be described in detail below based on drawings showing embodiments thereof. FIG. 1 is a circuit diagram showing an embodiment of the configuration of the present invention of an n-bit A/D converter using ladder resistors. Note that in FIG. 1, the same reference numerals as those in FIG. 2 described above indicate the same or corresponding parts. In FIG. 1, reference numeral 1 is a positive reference voltage input terminal, to which a voltage +VREF is input. 2 is the negative side reference voltage input terminal, and the voltage -VREF
has been entered. Between both positive side reference voltage input terminals 1 and 2, there are a resistor 3 with a resistance value of 1.5R, resistors 4a, 4b...4j, each with a resistance value of R, and resistors each with a resistance value of r. 4k, 4l, and a switch element circuit 4m in which a resistor 40 and a switch element 41 are connected in series, and the resistance value when the switch element 41 is turned on is about 0.5r. In addition, resistors 4a, 4b...4j
There are 2n −4 in total, and these and resistor 3, resistor 4
A ladder resistor is constituted by the resistors k, 4l and the switch element circuit 4m, and the total number of resistors is 2n. [0018] Each resistor 3, 4a, 4b...4j, 4k
, 4l, and 2n-1 between each of the switch element circuits 4m.
Intermediate taps 6a, 6 for taking out different comparison voltages
b...6m is provided and connected to the comparison circuit block 7. In this embodiment, a switch element circuit 5 in which a resistor 50 and a switch element 51 are connected in series is connected between the intermediate tap 6m and the negative reference voltage input terminal 2 as a side path, and the resistors 4k and 4l and the switch element circuit 4m are connected in parallel. The comparison circuit block 7 includes a selector that selects any one of the intermediate taps 6a, 6b, . It is composed of. Note that the analog input voltage is input to the comparison circuit block 7 from the analog input terminal 8. Also, comparison circuit block 7
A comparator output 10, which is the comparison result by the comparator, is given to the control block 9, and conversely, a control output 11 for controlling the selector and the comparator is given from the control block 9 to the comparison circuit block 7. There is. The control block 9 is composed of a control circuit for controlling the entire A/D converter, a register for storing the A/D conversion results, and the like. A comparison voltage enable/disable control signal 12 is sent from this control block 9 to the aforementioned switch elements 41 and 51 for simultaneously controlling on/off of the switch elements 41 and 51.
is given. Further, reference numeral 13 is an A/D converter control input/output given from the outside to the control block 9 for controlling the entire A/D converter, and 14 is an A/D conversion output from the control block 9 to the outside. This is the output. Conventional n-bit A/
The operation of the D converter is as follows. intermediate tap 6a,
The respective output voltages of 6b...6m should have a relationship as expressed by the following equation (1). Note that V(6i) (
However, i is a, b...m) is each intermediate tap 6a, 6b
...Indicates the output voltage of 6m. {+VREF −V(6a)}: {V(6a)
-V(6m)}:... {V(6k)
-V(6l)}:{V(6l)-V(6m)}:{V(
6m)-(-VREF)} = 1.5
:1:...:1:1:0.5
...(1) By the way, as mentioned above, each intermediate tap 6a
, 6b...6m are 1.5R, R,...r, r, 0.5r, respectively, but the resistance between the intermediate tap 6k and the negative reference voltage input terminal 2 whose input voltage is -VREF is A switch element circuit 5 in which a switch element 51 and a resistor 50 are connected in series is connected in parallel between them. The resistance value of the switch element 51 of this switch element circuit 5 when it is on is assumed to be ron. Here, the resistors 4k, 4l, 4m and 5
The combined resistance value between the intermediate tap 6k and the negative reference voltage input terminal 2 is {ron(r+r+ 1.5r)}/{ron+(r+
r+ 1.5r)}=R+R+1.5R, the above formula (1) is established, and a desirable output voltage can be obtained at each intermediate tap 6a, 6b, . . . , 6m. Now, when the A/D converter enable signal is input to the A/D converter control input/output 13 of the control block 9, the switch elements 41 and 51 are input from the control block 9.
The comparison voltage enable/disable control signal 12 output to the switching element 4 becomes enabled, and the switching element 4
1 and 51 are turned on. Next, the A/D converter control input/output 13
When the A/D conversion start signal is input, a control output 11 is output from the control block 9 to the comparison circuit block 7, and the comparison circuit block 7 compares the input voltage of the analog input terminal 8 with the input voltage of each intermediate tap 6a, 6b...6m. A comparator compares the output voltage with one of the output voltages selected by the control output 11 in the control block 9, and outputs the comparison result to the control block 9 as a comparator output 10. The control block 9 inputs the above-mentioned comparator output 10 and stores it in a register, and controls a selector to select the comparison voltage to be selected next based on it. By using the so-called binary search method that sequentially repeats such control, the n-bit
The A/D converter can obtain an A/D conversion result corresponding to the analog input voltage input from the analog input terminal 8 by performing n comparison operations. When the A/D conversion is completed, the control block 9
The A/D conversion result is output from the A/D conversion output 14 of. [0029] In addition, when A/D conversion is not performed,
When the A/D converter disable signal is input to the A/D converter control input/output 13, the comparison voltage enable/disable control signal 12 output from the control block 9 to the switch elements 41 and 51 is disabled. Therefore, switch elements 41 and 51 are turned off. Thereby, the current between both reference voltage input terminals 1 and 2 is cut off, and wasteful current consumption can be avoided. In the above embodiment, the switch element circuit 5 serving as a bypass is connected to the intermediate tap 6k, but it may be connected closer to the positive side reference voltage input terminal 1 side or closer to the negative side reference voltage input terminal 2 side. You may. In that case, the position at which the resistance value of the ladder resistor changes may be changed according to the connection position of the bypass, and the resistance value of the switch element circuit 5 on the side of the bypass may be adjusted as appropriate. Furthermore, in the above embodiment, the switch element circuit 4
m and 5 are switch elements 41 and 51 and resistor 4, respectively.
0 and 50, however, the required resistance may be obtained by switch elements 41 and 51, respectively. Furthermore, in the above embodiment, the switch element circuit 4
m and 5 are connected to the negative side reference voltage input terminal 2 side, but they may be connected to the positive side reference voltage input terminal 1 side. [0033] As described in detail above, part of the ladder resistors connected to the reference voltage source via the switch element is made to have a high resistance value, and a bypass is provided to bypass these resistors. Since the amount of current is compensated by the switch element and a switch element is also provided in the side path, it is possible to use an element with a high on-resistance value for the former switch element, and the switch element provided in the side path can also be Since there is no restriction on the intermediate tap voltage, it becomes possible to use elements with high on-resistance values. Therefore, since it is possible to use elements with high on-resistance values for both switch elements, it is possible to downsize the device and further reduce manufacturing costs.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of an A/D converter of the present invention.

FIG. 2 is a circuit diagram showing the configuration of a conventional A/D converter.

[Explanation of symbols]

1 Positive side reference voltage input terminal 2 Negative side reference voltage input terminal 3, 4a, 4b...4l Ladder resistance 4m
Switch element circuit 5 Switch element circuit 6a, 6b...6m Intermediate tap 41 Switch element 51 Switch element

Claims (1)

[Claims] 1. A ladder resistor connected between terminals to which two reference voltages are applied via switching elements controlled on/off, and a plurality of intermediate taps drawn out from the ladder resistor, In the A/D converter, the analog input voltage is converted into a digital signal by comparing the output voltage from each intermediate tap with the analog input voltage when the switch element is turned on. A side path having another switch element is provided in parallel with the switch element between one of the terminals, and the resistance value of the ladder resistor between the intermediate tap to which the side path is connected and the one terminal is set as a ladder. The resistance value is higher than that of other parts of the resistor, and both switch elements are turned on/off at the same time.
An A/D converter characterized by being configured to perform off control.