Coded data generation or conversion – Analog to or from digital conversion – Digital to analog conversion
Reexamination Certificate
2003-10-08
2004-11-30
Young, Brian (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Digital to analog conversion
C341S145000, C341S118000
Reexamination Certificate
active
06825787
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to a digital-to-analog converter and related control method, and more specifically, to a digital-to-analog converter and related method with ones complement current supply structure for simplifying control logic.
2. Description of the Prior Art
Digital-to-analog converters are a common and important structure in the modern electrical circuits. Generally speaking, digital data is much easier to be processed, saved and calculated. When presenting digital data, a digital-to-analog converter is needed to transform the digital data into an analog signal. For instance, a digital microprocessor is used in the control system for controlling the speed of a compact disk driven by a motor or how much power to supply to the pick-up head to write data to the compact disk. However, the digital data of the microprocessor first needs to be transformed to an analog signal by a digital-to-analog converter for controlling the motor rotation or controlling the power of the pick-up head.
Please refer to FIG.
1
.
FIG. 1
is a diagram of a prior art digital-to-analog converter
10
. The example in
FIG. 1
is a four-bit digital-to-analog converter. The converter
10
receives a four-bit input code
26
and provides an output voltage Vp as an analog output, the output voltage Vp corresponding to the input code
26
. The four-bit input code
26
comprises bits Ap
3
to Ap
0
, the bit Ap
3
being the most significant bit, the bit Ap
0
being the least significant bit. The converter
10
comprises a control logic
12
and an electrical module
14
. The input code
26
is transformed to a plurality of positive control bits Yp
0
to Yp
2
, negative control bits Xp
0
to Xp
2
and Co. The electrical module
14
provides a bias voltage by a direct current source Vcc and comprises a positive electrical module
16
A formed by a plurality of positive current sources
18
A to
18
C, a negative electrical module
16
B formed by a plurality of negative current sources
20
A to
20
C, a negative current source
20
D, a OP amp
24
, and a resistance R. Each positive and negative current source is electrically connected to a node Na through a switch
22
, and the resistance Rp is electrically connected between the node Na and the output node Nb of the OP amp
24
. By the virtual ground at the node Na of the OP amp
24
, the current flows through the resistance Rp for setting up the output voltage Vp. In the electrical module
14
, different positive and negative current sources provide different currents. The switch
22
is controlled by a corresponding positive control bit or negative control bit for providing a corresponding current to the node Na. As shown in
FIG. 1
, the negative current sources
20
A to
20
C provide the negative currents of 1I, 2I, 4I and 8I (the current I is a constant) according to ascending powers of two, the switches of the negative current sources being controlled by the negative control bits Xp
0
to Xp
2
and Co. The positive current sources
18
A to
18
C provide the positive currents of 1I, 2I, 4I and 8I similarly, the switches of the positive current sources being controlled by the positive control bits Yp
0
to Yp
2
. For instance, if the negative control bit is 1, the corresponding switch
22
is connected to the node Na, enabling the negative current source to provide a negative current of 1I to the node Na. On the contrary, if the negative control bit is 0, the corresponding switch
22
is off, stopping the negative current source from providing a negative current of 1I to the node Na. In other words, controlling the positive and negative control bits to be 0 or 1 controls the positive and negative current sources to be connected or not connected to the node Na for controlling the current flowing through the resistance Rp and for controlling the magnitude of the corresponding output voltage. The control logic
12
of the converter
10
encodes the input code as the positive and negative control codes to control the output voltage Vp generated by the electrical module
14
according to the input code
26
.
Please refer to
FIG. 2
(also refer to FIG.
1
).
FIG. 2
is a table
30
of the relationship between the input code
26
, the output voltage Vp and the positive and negative control bits. For instance, as shown in the table
30
, when the input code
26
(bits Ap
3
to Ap
0
) is “0001”, the converter
10
provides the output voltage Vp=1*I*Rp (abbreviated as 1IRp). When the input code
26
is “0110”, the output voltage will be 6IRp, and so on. In other words, the input code
26
represents a special value in binary, and the converter
10
provides an output voltage Vp with a direct proportion to the special value. As mentioned above, “0001” represents “1” and “0110” represents “6”. The converter
10
provides the corresponding voltages 1IRp and 6IRp. In digital arithmetic, a negative value is marked by 2s complement. Therefore, when the converter
10
receives the input code
26
in 2s complement, the converter
10
will provide a corresponding output voltage Vp. As shown in
FIG. 2
, when the input code
26
is “1111”, it represents “−1” by 2s complement, the converter
10
providing a negative voltage 1IRp. When the input code
26
is “1011”, it represents “−5” by 2s complement, the converter
10
providing a negative voltage 5IRp.
In order to establish the relationship between the input code and the output voltage in
FIG. 2
, the converter uses the positive and negative control bits to control the output voltage, connecting or not connecting the positive and negative current sources with the node Na. For instance, when the input code
26
is “0110”, the output voltage Vp is 6IRp, the positive control bits Yp
2
to Yp
1
being “1”, the positive current sources
18
B and
18
C separately providing 2I and 4I positive current to the node Na. There should be a 6IRp output voltage through the resistance Rp. At the same time, the other positive bit Yp
0
and the negative control bits Xp
2
to Xp
0
and Co are “0” for preventing the corresponding current sources from providing current to the node Na. Also, when the input code
26
is “1011”, the output voltage Vp is 5IRp, the positive control bits Yp
0
to Yp
2
being “0”, the negative control bits Xp
2
to Xp
0
and Co respectively being “1”,“0”,“1”, and “0”. The current sources
20
C and
20
A of the electrical module
14
separately provide negative current 4I and 1I to the node Na for establishing the output voltage Vp through the resistance Rp.
As shown in
FIG. 2
, when indicating negative values by 2s complement, the most significant bit Ap
3
of the input code
26
is a sign code. When the input code
26
represents a positive value or zero, the bit Ap
3
is “0”. When the input code
26
represents negative value by 2s complement, the bit Ap
3
is “1”. A value code
32
is formed by the other bits Ap
2
to Ap
0
of the input code
26
, the bits Ap
2
and Ap
0
respectively being the most and least significant bits. When the input code
26
represents a positive value, the value can be represented by Ap
2
*(2^2)+Ap
1
*(2^1)+Ap
0
*(2^0). Note that the positive current sources
18
C to
18
A in
FIG. 1
respectively provide 4I((2^2)I), 2I, and 1I current. Therefore, when the input code represents a positive value, the positive control bits Yp
2
to Tp
0
are respectively equal to the bits Ap
2
to Ap
0
(the negative control bits Yp
2
to Yp
0
and Co are “0”) for controlling the total current at the node Na to be in direct proportion to the value of the value code
32
, the total current provided by the positive current sources
18
A to
18
C, and the corresponding output voltage. The positive control bits Yp
2
and Yp
0
are respectively the most and least significant bits. A positive control code
28
A is formed by the control bits Yp
2
to Yp
0
.
As shown in
FIG. 1
, the negative current sources
20
A to
20
C respectively correspond to the positive current sources
18
A to
18
C, providing a m
Hsu Winston
Nguyen John B
VIA Technologies Inc.
Young Brian
LandOfFree
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