Current steering type D/A converter

Details Current steering type D/A converter Current steering type D/A converter

2002-05-29

2003-07-08

JeanPierre, Peguy (Department: 2819)

Coded data generation or conversion

Analog to or from digital conversion

Digital to analog conversion

C341S143000

Reexamination Certificate

active

06590516

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a current steering type D/A (digital-to-analog) converter to be used in a semiconductor integrated circuit and, more particularly, to an improved current steering type D/A converter containing plural circuit blocks.
BACKGROUND OF THE INVENTION
As an LSI grows in performance, there is an increasing need for a current steering type D/A converter mounted on the LSI chip to change its operation mode according to the use of the LSI, for example, to operate internal D/A conversion circuits in their normal states or power down states according to the use mode of the LSI.
FIG. 5
is a block diagram illustrating a conventional current steering type D/A converter
500
.
With reference to
FIG. 5
, the current steering type D/A converter
500
comprises a D/A conversion circuit
510
, a reference voltage generation circuit
520
, and a power down control circuit
530
. The D/A conversion circuit
510
comprises plural current sources
5101
each outputting a predetermined current, and a logic circuit
5102
for selecting required current sources corresponding to a digital input code, from among the plural current sources
5101
. The reference voltage generation circuit
520
outputs a reference voltage VB, and this reference voltage VB determines a current value IOUT to be outputted from a current output terminal DAOUT of the D/A conversion circuit
510
. A P channel MOS transistor constituting the power down control circuit
530
performs a switching operation for switching the current steering type D/A converter
500
between its normal state and power down state, according to a power down control signal supplied from a power down control terminal NPD.
Hereinafter, the operation of the current steering type D/A converter
500
constituted as described above will be described for its normal state and power down state.
First of all, when a “Low” signal (hereinafter referred to as a “L” signal) is inputted as a power down control signal to the power down control terminal NPD, the current steering type D/A converter
500
goes into the power down state. That is, the “L” signal inputted as the power down control signal brings the power down control circuit
530
into conduction, and a potential at a fixed potential node
560
is applied to a wiring
550
which connects a reference voltage VB node of the D/A conversion circuit
510
and a reference voltage node of the reference voltage generation circuit
520
. The fixed potential node
560
has previously been set at a potential that halts the current sources
5101
of the D/A conversion circuit
510
and the reference voltage generation circuit
520
. When this potential is applied to the D/A conversion circuit
510
and the reference voltage generation circuit
520
, the current sources
5101
of the D/A conversion circuit
510
and the reference voltage generation circuit
520
halt the operations.
Next, when a “High” signal (hereinafter referred to as a “H” signal) is inputted as a power down control signal to the power down control terminal NPD, the current steering type D/A converter
500
operates in the normal state. That is, the “H” signal inputted as the power down control signal brings the power down control circuit
530
into the non-conducting state, and the potential of the fixed potential node
560
is not applied to the wiring
550
. The reference voltage generation circuit
520
contains a power on control circuit (not shown) and a fixed potential node (not shown) corresponding to the power down control circuit
530
and the fixed potential node
560
, respectively, and the fixed potential node (not shown) is set at a voltage that operates the reference voltage generation circuit
520
. When the power on control circuit (not shown) receives the “H” signal, it transfers the voltage of the fixed potential node (not shown) to the main unit of the reference voltage generation circuit
520
. On receipt of the “H” signal as the power down control signal, the reference voltage generation circuit
520
outputs a reference voltage VB, and this voltage is supplied to the current sources
5101
of the D/A conversion circuit
510
. Subsequently, the logic circuit
5102
selects current sources corresponding to a digital input code, from among the plural current sources
5101
, and a current IOUT that is the sum of the currents of the selected current sources is outputted from the current output terminal DAOUT.
As described above, in the case where the single D/A conversion circuit
510
is provided corresponding to the single reference voltage generation circuit
520
, the MOS transistor
530
functioning as the power down control circuit switches the supply of power to the D/A conversion circuit
510
so that the D/A conversion circuit
510
goes into the normal state or the power down state.
Next, a description will be given of a conventional current steering type D/A converter in which plural D/A conversion circuits are provided corresponding to a single reference voltage generation circuit.
FIG. 6
is a block diagram illustrating a conventional current steering type D/A converter
600
having plural D/A conversion circuits. In
FIG. 6
, only two D/A conversion circuits are shown for the sake of simplicity.
With reference to
FIG. 6
, the current steering type D/A converter
600
comprises a first D/A conversion circuit
611
, a second D/A conversion circuit
612
, a reference voltage generation circuit
620
, and a power down control circuit
630
.
The first D/A conversion circuit
611
comprises plural current sources
6111
each outputting a predetermined current, and a first logic circuit
6112
for selecting required current sources corresponding to a digital input code, from among the plural current sources
6111
. The second D/A conversion circuit
612
comprises plural current sources
6121
each outputting a predetermined current, and a second logic circuit
6122
for selecting required current sources corresponding to a digital input code, from among the plural current sources
6121
. The reference voltage generation circuit
620
outputs a reference voltage VB, and the reference voltage VB determines a first current value IOUT
1
to be outputted from a first current output terminal DAOUT
1
of the first D/A conversion circuit
611
, as well as a second current value IOUT
2
to be outputted from a second current output terminal DAOUT
2
of the second D/A conversion circuit
612
. A P channel MOS transistor constituting the power down control circuit
630
performs a switching operation for switching the current steering type D/A converter
600
between its normal state and power down state, according to a power down control signal supplied from a power down control terminal NPD.
Hereinafter, the operation of the current steering type D/A converter
600
constituted as described above will be described for its normal state and power down state.
First of all, when a “L” signal is inputted to the power down control terminal NPD as a power down control signal, the current steering type D/A converter
600
operates in the power down state. That is, the “L” signal inputted as the power down control signal brings the power down control circuit
630
into conduction, and a potential of a fixed potential node
660
is supplied to a wiring
650
which connects the reference voltage VB nodes of the D/A conversion circuits
611
and
612
and the reference voltage VB node of the reference voltage generation circuit
620
. The fixed potential node
660
has previously been set at a potential that halts the current sources
6111
and
6121
of the D/A conversion circuits
611
and
612
and the reference voltage generation circuit
620
. When this potential is applied to the first and second D/A conversion circuits
611
and
612
and the reference voltage generation circuit
620
, the respective current sources
6111
and
6121
of the D/A conversion circuits
611
and
612
and the reference voltage generation circuit
620
halt the operations.
On the other hand, when a “H” sign

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