RSD analog to digital converter

Details RSD analog to digital converter RSD analog to digital converter

2001-12-04

2002-12-03

Wamsley, Patrick (Department: 2819)

Coded data generation or conversion

Analog to or from digital conversion

Analog to digital conversion

C341S120000

Reexamination Certificate

active

06489914

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to analog to digital (A/D) converters and more particularly to RSD A/D converters.
2. Related Art
RSD (redundant signed digit) A/D converters have been found to be effective for situations in which high speed is useful.
Referring to
FIG. 1
, a block diagram of a cyclic RSD A/D converter
10
, such as the one disclosed in U.S. Pat. No. 5,644,313, is shown. The A/D converter
10
includes an analog section having two RSD stages
11
and
12
followed by a digital section
14
having an alignment and synchronization block
15
and a correction block
16
. An analog input signal (voltage) is input to the first RSD stage
11
by way of a switch
18
. After the input signal is received, the switch
18
is opened. The first RSD stage
11
compares the input signal to a high voltage (VH) and a low voltage (VL) and generates a first digital output signal, in this case the msb, based on the comparison results. The first RSD stage
11
also generates a first residue voltage VR
1
. The msb is output to the digital section
14
and the residue voltage VR
1
is input to the second RSD stage
12
. The second RSD stage
12
also performs high and low voltage comparison operations, generates a second digital output signal (msb-
1
), and a second residue voltage VR
2
. The second digital output signal (msb-
1
) is output to the digital section
14
, the switch
18
is moved to connect the feedback path, and the second residue voltage VR
2
is provided to the first RSD stage
11
. This operation is repeated, with the RSD stages
11
,
12
outputting additional digital bits of the input signal. The digital bits are aligned, synchronized, and combined in the digital section
14
to provide a standard format binary output code.
In some applications, although speed is desired, it is also desirable for there to be high accuracy of the A/D converter. One of the difficulties in providing high precision in a RSD A/D converter is there required a high performance operational amplifier. The operational amplifier should have extremely gain and no offset voltage between the plus and minus inputs thereof. This is very difficult to achieve in practice. The offset voltage is a problem that results in reduced accuracy in the output. This error may be small but may become significant depending upon the application. It can be a limitation in the resolution of the A/D converter. Thus, there is a need for RSD converters with improved resolution.


REFERENCES:
patent: 5644308 (1997-07-01), Kerth et al.
patent: 5644313 (1997-07-01), Rakers et al.
Heubi, Micro Power ‘Relative Precision’ 13 bits Cyclic RSD A/D Converter, ISLPED 1996 Monterey, CA, pp. 253-257.

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