Amplifiers – Sum and difference amplifiers
Reexamination Certificate
2002-02-06
2004-07-13
Shingleton, Michael B (Department: 2817)
Amplifiers
Sum and difference amplifiers
C330S098000, C330S099000, C330S100000, C250S2140AG, C360S077020
Reexamination Certificate
active
06762644
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to transimpedance amplifiers, and more particularly to nested transimpedance amplifiers with an increased gain-bandwidth product.
BACKGROUND OF THE INVENTION
A transimpedance amplifier (TIA) is a well-known type of electronic circuit. Referring now to
FIG. 1
, a TIA
100
includes an operational amplifier (opamp)
105
having a gain parameter (g
m
). The opamp
105
is connected in parallel to a resistor (R
f
)
110
. The input to the TIA
100
is a current (&Dgr;i)
115
. The output of the TIA
100
is a voltage (&Dgr;v
o
)
120
.
Referring now to
FIG. 2
, the opamp
105
of the TIA
100
is replaced by a current source
205
and a transistor
210
having gain g
m
. The TIA
100
in
FIGS. 1 and 2
is often referred to as a transconductance amplifier because it converts the input current &Dgr;i into the output voltage &Dgr;v
o
.
Referring now to
FIG. 3
, a TIA
300
converts an input voltage (&Dgr;v
i
)
305
into an output voltage (&Dgr;v
o
)
310
. The TIA
300
also includes a resistor
315
that is connected to a transistor
320
. The TIA
300
is typically used in applications that require relatively low bandwidth.
Referring now to
FIG. 4
, a TIA
400
converts an input voltage (&Dgr;v
i
)
405
into an output voltage (&Dgr;v
o
)
410
. The TIA
400
includes a second opamp
415
, which is connected in series to a parallel combination of a resistor (R
f
)
420
and an opamp
425
. The TIA
400
is typically used for applications having higher bandwidth requirements than the TIA
300
.
Ordinarily, the bandwidth of the TIA is limited to a fraction of a threshold frequency f
T
of transistor(s) that are used in the opamp(s). In the case of a bipolar junction transistor (BJT) such as a . gallium-arsenide (GaAs) transistor, the bandwidth of the TIA is approximately equal to 10%-20% of f
T
. For metal-oxide-semiconductor (MOS) transistor(s), the bandwidth of the TIA is typically a few percent (i.e., approximately 2%-6%) of f
T
.
Referring now to
FIG. 5
, a TIA
500
may be configured to operate differentially using two inputs of each opamp
502
and
504
. One input
505
acts as a reference, in a similar manner as ground or virtual ground in a standard configuration TIA. The input voltage &Dgr;v
i
and the output voltage &Dgr;v
o
are measured as voltage differences between a reference input
505
and a second input
510
. Feedback resistors
514
and
516
are connected across the inputs and the outputs of the opamp
504
.
Referring now to
FIG. 6
, one TIA application having a relatively high bandwidth requirement is that of an optical sensor. An optical sensor circuit
600
includes the opamp
105
and the resistor
110
of the TIA
100
that are coupled with a photodiode
605
. The output of the photodiode
605
is a current I
photo
610
, which acts as an input to the TIA
100
.
Increasingly, applications require both high bandwidth and high gain. Examples include optical sensors, such as fiber optic receivers, and preamplifier writers for high-speed hard disk drives. Efforts to increase the gain-bandwidth product of TIAs have been made. For example, in U.S. Pat. No. 6,114,913, which are hereby incorporated by reference, a boost current is used to increase the gain-bandwidth product in the TIA. Cascading TIA stages is also used in U.S. Pat. Nos. 5,345,073 and 4,772,859, which are hereby incorporated by reference.
Other improvements to TIAs are the subject of other patents, such as U.S. Pat. Nos. 6,084,478; 6,057,738; 6,037,841; 5,646,573; 5,532,471; 5,382,920; 5,010,588; 4,914,402; 4,764,732; 4,724,315; 4,564,818; and 4,535,233, which are hereby incorporated by reference. However, improving the gain-bandwidth product of TIAs continues to be a challenge for circuit designers.
SUMMARY OF THE INVENTION
A nested transimpedance amplifier (TIA) circuit according to the present invention includes a zero-order TIA having an input and an output. A first operational amplifier (opamp) has an input that communicates with the output of the zero-order TIA and an output. A first feedback resistance has one end that communicates with the input of the zero-order TIA and an opposite end that communicates with the output of the first opamp.
In other features, a capacitor has one end that communicates with the input of the zero-order TIA. The zero order TIA includes a second opamp having an input and an output. A third opamp has an input that communicates with the output of the second opamp and an output. A second feedback resistance has one end that communicates with the input of the third opamp and an opposite end that communicates with the output of the third opamp.
In yet other features, a fourth opamp has an input and an output that communicates with the input of the second opamp. A fifth opamp has an input that communicates with the output of the first opamp and an output. A third feedback resistance has one end that communicates with the input of the fourth opamp and an opposite end that communicates with the output of the fifth opamp.
In still other features, at least one higher order circuit is connected to the nested TIA circuit and includes an n
th
feedback resistance, an n
th
opamp, and an (n+1)
th
opamp.
In yet other features of the invention, a nested differential mode TIA circuit includes a zero-order differential mode TIA having first and second inputs and first and second outputs: A first differential mode opamp has first and second inputs that communicate with the first and second outputs of the zero-order differential mode TIA and first and second outputs. A first feedback resistance has one end that communicates with the first input of the zero-order differential mode TIA and an opposite end that communicates with the first output of the zero-order differential mode TIA. A second feedback resistance has one end that communicates with the second input of the zero-order differential mode TIA and an opposite end that communicates with the second output of the zero-order differential mode TIA.
In still other features, the zero order differential mode TIA includes a second differential mode opamp having first and second inputs and first and second outputs. A third differential mode opamp has first and second inputs that communicate with the first and second outputs of the second differential mode opamp and first and second outputs. A third feedback resistance has one end that communicates with the first input of the third differential mode opamp and an opposite end that communicates with the first output of the third differential mode opamp. A fourth feedback resistance has one end that communicates with the second input of the third differential mode opamp and an opposite end that communicates with the second output of the third differential mode opamp.
In still other features, at least one higher order circuit is connected to the nested TIA circuit and includes an n
th
feedback resistance, an (n+1)
th
feedback resistance, and an n
th
differential mode opamp.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
REFERENCES:
patent: 4535233 (1985-08-01), Abraham
patent: 4564818 (1986-01-01), Jones
patent: 4724315 (1988-02-01), Goerne
patent: 4764732 (1988-08-01), Dion
patent: 4772859 (1988-09-01), Sakai
patent: 4914402 (1990-04-01), Dermitzakis et al.
patent: 5010588 (1991-04-01), Gimlett
patent: 5345073 (1994-09-01), Chang et al.
patent: 5382920 (1995-01-01), Jung
patent: 5532471 (1996-07-01), Khorramabadi et al.
patent: 5646573 (1997-07-01), Bayruns et al.
patent: 6037841 (2000-03-01), Tanji et al.
patent: 6057738 (2000-05-01), Ku et al.
patent: 6084478 (2000-07-01), Mayampurath
patent: 6114913 (2000-09-01), Entrikin
patent: 6122131 (2000-09-01), Jeppson
patent: H6-61752 (1994-03-01), No
Marvell International Ltd.
Shingleton Michael B
LandOfFree
Apparatus and method for a nested transimpedance amplifier does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for a nested transimpedance amplifier, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for a nested transimpedance amplifier will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3196121