Analog integrator circuit

Details Analog integrator circuit Analog integrator circuit

2000-07-07

2002-12-31

Nuton, My-Trang (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Specific input to output function

By integrating

C327S337000, C327S344000

Reexamination Certificate

active

06501322

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to the field of analog circuits, and in particular to the field of analog integrator circuits, suitable for use for example with an analog-to-digital converter (ADC).
FIGS. 4 and 5
illustrate analog integrator circuits suitable for use with an ADC. The integrator circuit illustrated in
FIG. 4
includes a transconductance amplifier V, whose output is fed back via an integration capacitor Ci to its inverting input. A reference voltage V
2
is applied to the non-inverting input of the amplifier V. A reference voltage V
1
is applied to a series circuit consisting of an adjustable resistor R
1
and a current source Q
1
with a parallel parasitic capacitor Cp. The common connection point of the adjustable resistor R
1
and the current source Q
1
is connected to the inverting input of the transconductance amplifier V.
FIG. 5
illustrates an integrator in which the adjustable resistor is realized as a switched capacitor C
1
. This integrator therefore can be integrated in a space-saving manner.
The integrator circuits illustrated in
FIGS. 4 and 5
are used, for example, in ADCs. The adjustable resistor R
1
and the switched capacitor C
1
are adjusted, depending on the voltage Vo at the output of the transconductance amplifier, in such a way that the current flowing through the adjustable resistor takes up the input current from the current source.
A problem with conventional analog integrator circuits occurs when the parasitic parallel input capacitance is large. For example, referring still to
FIGS. 4 and 5
, if the device providing the input signal to the ADC is a integrated photodiode PD, the photodiode PD generally has a relatively high parasitic parallel input capacitance Cp. As a consequence of the large parallel parasitic capacitance Cp and low input current, the ratio of the parallel parasitic capacitance Cp to the integration capacitance Ci (i.e., Cp/Ci) is about one-hundred. As a result, the amplification-bandwidth product is undesirably reduced by about two orders of magnitude.
When using a switched capacitance as the adjustable resistance, the bandwidth should be large enough, while at the same time the DC amplification likewise should be large, in order to ensure that the integrator circuit functions even at low frequencies. However, because these two requirements are contradictory, a compromise between them is necessary in order to achieve an acceptable bandwidth and an acceptable DC amplification.
Therefore, there is a need for an analog integrator circuit that provides the requisite bandwidth and DC amplification.
SUMMARY OF THE INVENTION
Briefly, according to the present invention, a voltage divider that includes a first and a second resistor and a current source with the parallel parasitic capacitance that together provide a second reference voltage. The connection point of the first and of the second resistor is connected to the inverting input of a transconductance amplifier.
The second resistor, which does not exist in the prior art, is dimensioned such that the ratios of the feedback network
j
⁢
 
⁢
ω
⁢
 
⁢
Ci
(
R2
+
j
⁢
 
⁢
ω
⁢
 
⁢
Cp
)
are changed in such a way that a much higher amplification-bandwidth product is achieved.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of preferred embodiments thereof, as illustrated in the accompanying drawings.


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patent: 5832085 (1998-11-01), Inoue et al.
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patent: 6160435 (2000-12-01), Kim
patent: 27 32 298 (1979-02-01), None

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