High bandwidth transresistance amplifier

Details High bandwidth transresistance amplifier High bandwidth transresistance amplifier

2000-08-23

2003-05-20

Pascal, Robert (Department: 2817)

Amplifiers

With semiconductor amplifying device

Including current mirror amplifier

C330S257000

Reexamination Certificate

active

06566955

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
This invention relates in general to transresistance amplifiers (also referred to as “I/V amplifiers” or “current-to-voltage amplifiers”) and, more specifically, to high bandwidth transresistance amplifiers.
BACKGROUND OF THE INVENTION
As shown in
FIG. 1
, a conventional transresistance amplifier
10
used, for example, in a CD or DVD-ROM application includes a photo-diode
12
that receives laser light reflected off a CD or DVD-ROM disc. In response to the laser light, the photo-diode
12
generates an input current I
i
. An operational amplifier
14
and a feedback resistor R
F
then convert the input current I
i
into a voltage signal represented by an output voltage V
o
. Specifically,
V
0
≈I
i
·R
F
+V
REF
  (1)
where V
REF
is a reference voltage (e.g., ground) at the non-inverting input of the operation amplifier
14
, and the gain of the amplifier
14
is assumed to be infinite.
Unfortunately, the photo-diode
12
typically has a relatively large parasitic capacitance C
p
(about 2.5 pF) associated with it. As a result, the operational amplifier
14
has a dominant parasitic-capacitance-induced pole at its inverting input, which limits the bandwidth of the transresistance amplifier
10
to about 100 MHz. This limited bandwidth, in turn, tends to distort the voltage signal output from the amplifier
10
, which makes the voltage signal harder to read and increases the possibility it will be read incorrectly.
Accordingly, there is a need in the art for an increased bandwidth transresistance amplifier.
SUMMARY OF THE INVENTION
In accordance with this invention, a circuit (e.g., a transresistance amplifier) for generating an output voltage from an input current includes a current amplifier that generates an amplified current in response to a bias current drawn from the current amplifier. Also, a current buffer includes an input node in communication with the input current, a current source that draws current from the input node, a buffering amplifier that has an input connected to the input node and an output that outputs a buffered voltage, and a buffering device for regulating the flow of bias current from the current amplifier to the input node in response to the buffered voltage. Further, an I/V amplifier coupled to the current amplifier receives the amplified current and generates the output voltage in response.
In another embodiment of this invention, an output voltage is generated from an input current when the input current is buffered by varying the output of a differential amplifier in accordance with the input current, and then varying the current flowing through a buffering device in accordance with the varying output of the differential amplifier. Also, the current flowing through the buffering device is amplified, and the output voltage is generated from the amplified current using a transresistance amplifier.


REFERENCES:
patent: 4333141 (1982-06-01), Nagano
patent: 4713628 (1987-12-01), Nelson
patent: 5157322 (1992-10-01), Llewllyn
patent: 5212457 (1993-05-01), Frey et al.
patent: 5424682 (1995-06-01), Gomez et al.
patent: 5589798 (1996-12-01), Harvey

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