JP2001267926A - Digital-to-analog converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current cell type digital/analog converter by which the level of an output analog voltage can easily be adjusted without deteriorating the precision of digital/analog conversion. SOLUTION: In the digital/analog converter, the difference current IS between a current ICS flowing through a MOS transistor(TR) 102 acting like a constant current source and a current ISET flowing through a resistor RSET to generate a monitor voltage given to an operational amplifier 101 is adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a DA converter for converting digital input data into an analog output voltage, and more particularly to a current cell type DA converter.

[0002]

2. Description of the Related Art For example, a current cell type DA converter is used as a high-speed DA converter used for a video rate.

FIG. 4 is a schematic circuit diagram of a current cell type DA converter.

[0004] The DA converter 10 is an LSI 100
And two external resistors R _SET and R _OUT . In the LSI 100, an operational amplifier 101, a MOS transistor 102 forming a constant current source, and (2 ⁿ -1) (n is a digital data Output generating MOS transistor 103 and output generating MO
It comprises a switch 104 that switches between the S-transistor 103 and the output terminal 100c.

The operational amplifier 101 has a reference voltage input terminal 1
00a, a reference voltage V _REF is inputted from outside and a MOS transistor 10 constituting a constant current source.
Current flowing through the 2 I _CS is connected to the terminal 100b resistor R
_The monitor voltage is converted by _SET and the monitor voltage is input to the operational amplifier 101. The operational amplifier 101 controls the gate voltage of the MOS transistor 102 as a constant current source so that the monitor voltage becomes equal to the reference voltage.

A MOS transistor as the constant voltage source
102 and (2) for output generationⁿ-1) MOS transistors
The star 103 constitutes a mirror circuit.
(2) for outputⁿ-1) MOS transistors 1
03 flows through the MOS transistor 102
The current corresponding to the current flows. Then, those (2 ⁿ
-1) MOS transistors 103 and output terminal 100
switch 104 placed on the path connecting
Digital data by connecting and disconnecting according to digital data.
Current flows from the output terminal 100c according to the data
And the resistance R_OUTIs converted to an output analog voltage.

Here, only one MOS transistor 102 as a constant current source is shown here for the sake of principle explanation. However, in general, in order to compensate for variations in characteristics depending on the location in one LSI 100. MOS transistors at a plurality of positions at different locations are connected in parallel and used as a constant current source.

[0008]

Here, the adjustment of the output analog voltage caused by the error of the resistance shown in FIG.
In order to obtain an output analog voltage corresponding to a circuit connected to the subsequent stage of the conversion device 10, it is desired to fine-tune or arbitrarily set an output analog voltage for input digital data.

Since the output analog voltage is proportional to the reference voltage V _REF , the reference voltage V
It is conceivable to change _REF, but changing this reference voltage V _REF will change the operating point of the constant current source, thus deteriorating the linearity of the change of the output analog voltage with respect to the change of input digital data. It will cause it.

The output analog voltage is supplied to the output terminal 10.
Since also proportional to the resistance value of the resistor R _out is connected to 0c, compared with the resistance R _out by a variable resistor it is also tentatively believed to be configured to adjust the resistance value, the variable resistor and the fixed resistor The parasitic capacitance is large, and it is difficult to obtain the target performance if the resistance R _out is variable.

Japanese Unexamined Patent Publication No. 8-274462 discloses a MOS transistor 1 shown in FIG.
A technique of changing the monitor voltage of the node corresponding to the terminal 100b in FIG.

However, the MOS transistor 102 as the constant current source shown in FIG. 4 is usually composed of a plurality of MOS transistors, because, as described above, it is necessary to compensate for variations in the characteristics of the LSI 100 from place to place. However, if some of them are turned on and off and adjusted as proposed in the above-mentioned publication, there is a possibility that the variation at each location may not be compensated correctly.

In view of the above circumstances, an object of the present invention is to provide a DA converter capable of adjusting an output analog voltage for input digital data while maintaining performance.

[0014]

According to the present invention, there is provided a D / A converter for converting digital input data into an analog output voltage, wherein the first current is used to convert a current into a monitor voltage. A voltage conversion circuit, a first current source connected to the first current-voltage conversion circuit for generating a current adjusted according to the control signal, and a first current-voltage conversion circuit for receiving a reference voltage from outside and performing a first current-voltage conversion A control circuit that inputs a monitor voltage obtained by the circuit and outputs a control signal to the first current source so that the monitor voltage becomes a voltage corresponding to the reference voltage; and converts the current to an output voltage. A second current-to-voltage conversion circuit connected to the second current-to-voltage conversion circuit for generating a current corresponding to the current generated by the first current source and corresponding to the input data; The first And an adjustment circuit for adjusting a difference current between the current generated by the first current source and the current converted to the monitor voltage by the first current-voltage conversion circuit. It is characterized by.

Here, in the DA converter according to the present invention, the adjusting circuit may be composed of an adjustable constant current source for generating the differential current, or the adjusting circuit may be adjustable. A constant voltage source, and a resistor disposed between the constant voltage source and the first current / voltage circuit. And an adjustment DA converter that generates a difference current according to

[0016] The DA converter according to the present invention comprises the above adjustment circuit.
, The reference voltage V_{RE F}And resistance R_SET, R
_outThe monitor voltage can be adjusted without changing
And therefore an output analyzer for the input digital data.
The log voltage can be adjusted.

[0017]

Embodiments of the present invention will be described below.

FIG. 1 is a schematic configuration diagram of a first embodiment of a DA converter according to the present invention. In FIG. 1 and each of the drawings described below, the same components as those of the conventional example shown in FIG. 4 are denoted by the same reference numerals as those of FIG. explain.

The DA converter 10 shown in FIG.
A constant current source 200 is provided.
Adjustment current I generated by_SIs the adjustment current input terminal 100
d, and flows through the MOS transistor 102.
Current I_CSAnd the resistance R_SETFlows to Accordingly
Adjustment current I generated by lever constant current source 200_SAdjust
Then, the monitor power input to the operational amplifier
The voltage is adjusted, and therefore the MOS transistor 102
The gate voltage is adjusted so that the MOS transistor 102
Current I flowing through_CSIs adjusted, and (2)ⁿ-1) pieces
Current of each MOS transistor 103 is adjusted
As a result, the output analog voltage is adjusted. This place
If the reference voltage V_REFIs unchanged and the two
Anti-R_SET, R_{ou t}Output output without adjusting or changing
The analog voltage is adjusted.

In the embodiment shown in FIG. 1, the resistor R _SET corresponds to the first current-voltage conversion circuit according to the present invention, the MOS transistor 102 corresponds to the first current source according to the present invention, The operational amplifier 101 corresponds to the control circuit according to the present invention, the resistor R _out corresponds to the second current-voltage conversion circuit, and the (2 ⁿ -1) MOS transistors 1 for output are used.
The combination of the switch 03 and the switch 104 corresponds to the second current source according to the present invention, and the constant current source 200 corresponds to the adjusting circuit according to the present invention.

Here, when the adjustment current I _S = 0, I _CS = V _REF / R _SET I _CS = I _SET , and the current when all (2 ⁿ -1) switches 104 are turned on. (Full-scale current) I _FS is (2 ⁿ
Assuming that the current flowing through each of the -1) output MOS transistors 103 is equal to the current I _CS flowing through the MOS transistor 102, I _FS = I _CS · (2 ⁿ −1) = (V _REF / R _SET ) (2 ⁿ -1)... (1) holds, for example, when I _S = 0.5 × (V _REF / R _SET ) is passed as the adjustment current I _S , I _SET = (V _REF / R _SET ) I _CS = I _SET -I _S = (V _REF / R _SET ) −0.5 × (V _REF / R _SET ) = 0.5 × (V _REF / R _SET ) I _FS = 0.5 × (V _RET / R _SET ) · (2 ⁿ −1) (2), and the full-scale voltage _IFS is adjusted by half, and the full-scale voltage at that time is also adjusted by half.

FIG. 2 is a schematic circuit diagram of a DA converter according to a second embodiment of the present invention.

FIG. 2 shows a constant current source 200 shown in FIG.
, A variable voltage constant voltage source 201 and a resistor R _S are connected.

Also in this case, the adjustment current I _S for changing the voltage level of the constant voltage source 201 changes, so that the output analog voltage can be adjusted.

FIG. 3 is a schematic circuit diagram of a DA converter according to a third embodiment of the present invention.

Here, FIG. 1 and FIG.
Circuit configuration part 1 corresponding to the circuit configuration in the LSI
In addition to 00A, another second circuit component 100B having a similar configuration is constructed. The second circuit component 100B also forms one DA converter, and when the on / off of the switch 104 'is adjusted, the current I _S toward the resistor R _SET can be adjusted. This switch 10
On / off of 4 'may be performed by inputting digital data for on / off from the outside, or a register or the like may be provided inside and data may be stored in advance therein.

As described above, the MOS transistor 102
A current I _CS flowing, the method of adjusting the differential current I _S of the current I _SET flowing through the resistor R _SET There are several methods may adjust the difference current I _S in any way.

[0028]

As described above, according to the present invention, the level of the output analog voltage can be easily adjusted without deteriorating the accuracy of DA conversion.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of a DA converter according to the present invention.

FIG. 2 is a schematic circuit diagram of a DA converter according to a second embodiment of the present invention.

FIG. 3 is a schematic circuit diagram of a DA converter according to a third embodiment of the present invention.

FIG. 4 is a schematic circuit diagram of a current cell type DA converter.

[Explanation of symbols]

 Reference Signs List 10 DA converter 100 LSI 100A First circuit component 100B Second circuit component 100a Reference voltage input terminal 100b Terminal 100c Output terminal 101 Operational amplifier 102 MOS transistor 103 Output generation MOS transistor 104, 104 'switch 200 Constant current source 201 constant voltage source

Claims (4)

[Claims] 1. A DA converter for converting digital input data into an analog output voltage, a first current-voltage conversion circuit for converting a current into a monitor voltage, and a current adjusted in accordance with a control signal. , The first
A first current source connected to the current / voltage conversion circuit, and a reference voltage input from outside and a monitor voltage obtained by the first current / voltage conversion circuit, and the monitor voltage is applied to the reference voltage. The first voltage is adjusted to a voltage corresponding to the first voltage.
A control circuit that outputs a control signal toward the current source, a second current-voltage conversion circuit that converts a current into an output voltage, and a current corresponding to the current generated by the first current source. And a second current source connected to the second current-voltage conversion circuit for generating a current corresponding to the input data; a current generated by the first current source; An adjustment circuit for adjusting a difference current between the conversion current and a current converted to a monitor voltage by the conversion circuit. 2. The DA converter according to claim 1, wherein the adjustment circuit comprises an adjustable constant current source that generates the difference current. 3. The adjustment circuit according to claim 1, wherein the adjustment circuit comprises an adjustable constant voltage source and a resistor disposed between the constant voltage source and the first current voltage circuit. The DA converter according to the above. 4. The DA converter according to claim 1, wherein said adjusting circuit comprises an adjusting DA converter for generating a difference current according to the adjusting digital data.