Selecting circuit, digital/analog converter and...

Details Selecting circuit, digital/analog converter and... Selecting circuit, digital/analog converter and...

2001-03-27

2002-04-02

Tokar, Michael (Department: 2819)

Coded data generation or conversion

Analog to or from digital conversion

Digital to analog conversion

C341S141000, C341S150000, C341S154000, C341S155000, C341S143000, C341S118000, C341S120000, C341S153000

Reexamination Certificate

active

06366228

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-088411, filed Mar. 28, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
This invention relates to a selecting circuit. More particularly, the present invention relates to a selecting circuit to be used for selecting CMOS inverters or constant-current sources in a D/A (digital/analog) converter or an A/D (analog/digital) converter.
Firstly, a D/A converter disclosed in U.S. Pat. No. 5,138,317 will be described as a known D/A converter.
Referring to
FIG. 1
of the accompanying drawings, a D/A converter described in the above patent document is adapted to thermometer-decode an n (positive integer)-bit digital data into 2
n
data (Step A) and convert the 2
n
data obtained by the thermometer-decoding into 2
n
data by DWA (data weighted averaging)-decoding (Step B) on the basis of a rearrangement algorithm circuit. Then, the 2
n
data obtained by the DWA-decoding is used to select CMOS inverters or constant-current sources (Step C).
The DWA-decoding operation is carried out by a selecting circuit (rearrangement algorithm circuit). The selecting circuit selects CMOS inverters or constant-current sources on the basis of a rearrangement algorithm. More specifically, the selecting circuit thermometer-decodes the n-bit data to generate a 2
n
-valued data (2
n
−1≧m≧0) and rearranges the 2
n
-valued data (by DWA-decoding) on the basis of the rearrangement algorithm so that it selects a total of m CMOS inverters or constant-current sources that are controlled by the selected m lines on the basis of the 2
n
-valued data. Then, the electric currents of the selected constant-current sources (i) are added (m×i) and the obtained result is converted into a voltage by an I-V converter circuit to produce the desired analog data.
Now, methods that can be used for selecting CMOS inverters or constant-current sources will be discussed below.
The technique of thermometer-decoding as shown in Table 1 (3 bits→5 values) and Table 2 (3 bits→7 values) is known for selecting CMOS inverters or constant-current sources. This technique is characterized in that a predetermined number of constant-current sources are selected from a side of plurality of constant-current sources that are always arranged side by side like a thermometer for each data conversion.
TABLE 1
Thermometer Cording
Selected: ∘
5-Values
output signal
DATA
1
2
3
4
+2
4
∘
∘
∘
∘
−1
1
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
0
2
∘
∘
&Circlesolid;
&Circlesolid;
+1
3
∘
∘
∘
&Circlesolid;
+2
4
∘
∘
∘
∘
−1
1
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
−2
0
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
0
2
∘
∘
&Circlesolid;
&Circlesolid;
+1
3
∘
∘
∘
&Circlesolid;
0
2
∘
∘
&Circlesolid;
&Circlesolid;
−2
0
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
0
2
∘
∘
&Circlesolid;
&Circlesolid;
−1
1
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
+2
4
∘
∘
∘
∘
+1
3
∘
∘
∘
&Circlesolid;
−2
0
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
−1
1
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
+1
3
∘
∘
∘
&Circlesolid;
−2
0
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
0
2
∘
∘
&Circlesolid;
&Circlesolid;
−1
1
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
+2
4
∘
∘
∘
∘
−2
0
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
+1
3
∘
∘
∘
&Circlesolid;
−1
1
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
0
2
∘
∘
&Circlesolid;
&Circlesolid;
+2
4
∘
∘
∘
∘
+1
3
∘
∘
∘
&Circlesolid;
0
2
∘
∘
&Circlesolid;
&Circlesolid;
TABLE 2
Thermometer Cording
7 Values
Selected: ∘
output signal
DATA
1
2
3
4
5
6
+2
5
∘
∘
∘
∘
∘
&Circlesolid;
−1
2
∘
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
  0
3
∘
∘
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
+1
4
∘
∘
∘
∘
&Circlesolid;
&Circlesolid;
+3
6
∘
∘
∘
∘
∘
∘
+2
5
∘
∘
∘
∘
∘
&Circlesolid;
−2
1
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
  0
3
∘
∘
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
+1
4
∘
∘
∘
∘
&Circlesolid;
&Circlesolid;
−3
0
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
−2
1
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
  0
3
∘
∘
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
−1
2
∘
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
+3
6
∘
∘
∘
∘
∘
∘
+2
5
∘
∘
∘
∘
∘
&Circlesolid;
−2
1
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
−1
2
∘
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
+1
4
∘
∘
∘
∘
&Circlesolid;
&Circlesolid;
−2
1
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
  0
3
∘
∘
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
−1
2
∘
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
+3
6
∘
∘
∘
∘
∘
∘
−3
0
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
+2
5
∘
∘
∘
∘
∘
&Circlesolid;
−1
2
∘
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
−3
0
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
+3
6
∘
∘
∘
∘
∘
∘
+2
5
∘
∘
∘
∘
∘
&Circlesolid;
  0
3
∘
∘
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
−3
0
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
&Circlesolid;
+1
4
∘
∘
∘
∘
&Circlesolid;
&Circlesolid;
There is also known a technique of selecting a plurality of constant-current sources with a same probability in order to noise-shaping the errors (noise) in the electric currents that are generated in a plurality of constant-current sources.
Table 3 (3 bits→5 values) and Table 4 (3 bits→7 values) show a selection method referred to as DWA-decoding (data weighted averaging-decoding).
This method is characterized in that constant-current sources are sequentially selected from a side of a plurality of constant-current sources that are arranged side by side to the other side. With this technique, as an operation of data conversion is repeated, constant-current sources are sequentially selected from a side of a plurality of constant-current sources to the other side and, when a constant-current source is selected as one closest to the extremity of the other side, one closest to the extremity of this side is selected so that the selected constant-current sources runs circularly.
TABLE 3
DWA Cording
Selected : ∘
5-Values
output signal
DATA
1
2
3
4
+2
4
∘
∘
∘
∘
−1
1
∘
&Circlesolid;
&Circlesolid;
&Circlesolid;
0
2
&Circlesolid;
∘
∘
&Circlesolid;
+1
3
∘
∘
&Circlesolid;
∘
+2
4
∘
∘
∘
∘
−1
1
&Circlesolid;
&Ci

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