Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
2002-03-11
2003-05-13
Le, Dinh T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C330S009000
Reexamination Certificate
active
06563348
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to electronic circuits and, more specifically, the present invention relates to sampling signals with electronic circuits.
2. Background Information
In the electronic circuit industry, there is a continuing effort to increase circuit speeds as well as decrease circuit device sizes. As circuit designs become more advanced, circuits become faster, smaller and are able to operate with less voltage and power. In switched-capacitor circuitry, there is technique known as double-sampling, which enables faster analog-to-digital conversion.
To illustrate,
FIG. 1
is circuit
101
illustrating double-sampling using switched-capacitor circuitry. As shown, circuit
101
includes an operational amplifier (op-amp)
103
having a non-inverting input coupled to ground and an inverting input coupled to sample and hold (S/H) circuit
105
and S/H circuit
107
. S/H circuits
105
and
107
are a type of switched-capacitor circuit and are coupled to alternatingly sample an input signal vin during opposite phases of a clock signal. As shown, S/H circuit
105
is coupled to the inverting input of op-amp
103
through switch
123
. S/H circuit
107
is also coupled to the same inverting input of op-amp
103
through switch
137
.
In operation, switch
123
is closed while switch
137
is opened, and switch
137
is closed while switch
123
is opened. During normal operation, switches
123
and
137
are never both closed or opened simultaneously. When input signal vin is being sampled by S/H circuit
105
, switches
117
,
119
and
121
are closed and switches
123
,
125
,
127
and
129
are opened so that the input signal vin is sampled onto capacitors
111
and
109
. When S/H circuit
105
is evaluated by op-amp
103
, switches
117
,
119
,
121
and
129
are opened and switches
123
,
125
and
127
are closed so that the voltage stored on capacitor
111
is evaluated by op-amp
103
through the switched connection provided by switch
123
and capacitor
109
provides a feedback capacitor coupled to the output of op-amp
103
.
Similarly, when input signal vin is being sampled by S/H circuit
107
, switches
131
,
133
and
135
are closed and switches
137
,
139
,
141
and
143
are opened so that the input signal vin is sampled onto capacitors
113
and
115
. When S/H circuit
107
is evaluated by op-amp
103
, switches
131
,
133
,
135
and
143
are opened and switches
137
,
139
and
141
are closed so that the voltage stored on capacitor
115
is evaluated by op-amp
103
through the switched connection provided by switch
137
and capacitor
113
provides a feedback capacitor coupled to the output of op-amp
103
.
The idea behind double-sampling is that in an analog switched-capacitor system, twice the amount of data can be processed if two sets of analog sampling circuitry are interleaved. Known double-sampling approaches are based upon the ability to switch in and out two identical sampling stages, such as S/H circuits
105
and
107
through switches
123
and
137
, respectively. The switching action of switches
123
and
137
reduces the overall performance of circuit
101
and as technology improves and supply voltages are scaled down, double-sampling is virtually unusable in low-voltage or low gain designs.
Known problems with circuit
101
include the fact that the inverting input of op-amp
103
is never discharged between evaluations of S/H circuits
105
and
107
. Consequently, residual charge from a previous evaluation is left on the inverting input of op-amp
103
to taint or contaminate a subsequent evaluation. Another problem that limits the performance of circuit
101
is that the capacitive loads of S/H circuits
105
and
107
are both tied to the inverting input of op-amp
103
. In particular, it is appreciated that even though switches
123
and
137
are never both closed simultaneously during normal operation, the capacitive loads of S/H circuits
105
and
107
are nevertheless both capacitively coupled to the inverting input of op-amp
103
since switches
123
and
137
are implemented with transistors. As a result, the maximum switching speeds of circuit
101
are reduced due to the relatively large capacitive load coupled to the inverting input of op-amp
103
SUMMARY OF THE INVENTION
Methods and apparatuses for a double-sampling a signal are disclosed. In one embodiment, a circuit according to the teachings of the present invention includes an op-amp having four input terminals. Two of the input terminals are tied to ground and the other two terminals are coupled to S/H circuits through unswitched connections. The S/H circuits are coupled to sample an input signal. Since the connections to the S/H circuits are not switched, the problems associated with having to switch in and out the S/H circuits that plague the prior art double-sampling techniques are reduced. Additional features and benefits of the present invention will become apparent from the detailed description and figures set forth below.
REFERENCES:
patent: 4460874 (1984-07-01), Haque
patent: 5248974 (1993-09-01), Fattaruso et al.
Allstot David J.
Beck Douglas R.
Blakely Sokoloff Taylor & Zafman LLC
Le Dinh T.
University of Washington
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