Amplifiers – With semiconductor amplifying device – Including atomic particle or radiant energy impinging on a...
Reexamination Certificate
2003-04-18
2004-09-07
Nguyen, Patricia (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including atomic particle or radiant energy impinging on a...
C330S278000, C330S285000, C250S2140AG
Reexamination Certificate
active
06788152
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2002-118233, filed on Apr. 19, 2002, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to an amplification circuit, and more specifically relates to an amplification circuit provided in an optical communication apparatus.
In recent years, electronic devices such as portable telephones, and portable terminals such as personal digital assistants (PDAs) have been provided with infrared data communication functions. Computers have been provided with optical communication apparatuses for sending and receiving data over optical fiber. These optical communication apparatuses include an amplification circuit as an optical receiver amplifier (amp).
As shown in
FIG. 1
, a first example of a conventional optical receiver amp
10
is connected to a photodiode PD. The photodiode PD generates a reception current IPD corresponding to the amount of light received, and the optical receiver amp
10
generates a reception signal RX in accordance with the reception current IPD. The optical receiver amp
10
includes a pre-amp
11
, a main amp
12
, and a comparator
13
.
The pre-amp
11
includes a resistor R
1
connected between an operating power supply VREG and the photodiode PD, and a diode D
1
connected in parallel with the resistor R
1
. The diode D
1
is connected to the resistor R
1
in the forward direction relative to the current flowing through the resistor R
1
. The pre-amp
11
converts the reception current IPD to a voltage signal VFM. The amount of change &Dgr;VFM of the voltage signal VFM relative to the amount of change &Dgr;IPD of the reception current IPD is represented by the expression &Dgr;VFM=&Dgr;IPD×R
1
. The operating power supply VREG may supplied through a power supply filter provided internally or externally to an integrated circuit (IC) built into the receiver amp
10
, or may be supplied from a constant-voltage regulated power supply.
The main amp
12
amplifies the voltage signal VFM, and generates an amplification signal VA. The comparator
13
converts the amplification signal VA of the main amp
12
to a digital reception signal RX using a threshold voltage VTH.
An optical receiver amp
20
of a second conventional example is a differential-type amp, as shown in
FIG. 2
, and includes a pre-amp
21
, a buffer circuit
22
, a bandpass filter
23
, a main amp
24
, a comparator
25
, and a DC light-canceling circuit
26
.
The pre-amp
21
includes two resistors R
2
and R
3
, four transistors Q
1
through Q
4
, and two current sources
27
and
28
, and generates a differential output signal. The resistor R
2
, transistor Q
1
and current source
27
are connected in series between an operating power supply VREG and a low-potential power supply, and the resistor R
3
, transistor Q
2
and current source
28
are connected in series between the operating power supply VREG and the low-potential power supply. A bias voltage VB is supplied to the bases of the transistors Q
1
and Q
2
. A photodiode PD is connected at a node between the transistor Q
1
and the current source
27
.
The emitter of the transistor Q
3
is connected between the resistor R
2
and the transistor Q
1
, and the emitter of the transistor Q
4
is connected at the node between the resistor R
3
and the transistor Q
2
. A high-potential power supply Vcc supplies power to the collectors of the transistors Q
3
and Q
4
, and a clamp voltage Vc is applied to the bases of the transistors Q
3
and Q
4
.
The pre-amp
21
generates a main voltage signal VFM at a node between the resistor R
2
and the transistor Q
1
, and generates a reference voltage signal VFP at a node between the resistor R
3
and the transistor Q
2
.
When a reception current is not generated by the photodiode PD, the clamp voltage Vc, and base-emitter voltage VBE of the transistors Q
3
and Q
4
, and the voltage signal VFM have the relationship VC−VBE>VFM, and the transistors Q
3
and Q
4
are turned OFF. The transistors Q
3
and Q
4
are turned ON when a relatively large input current is supplied, and the voltage signals VFM and VFP are clamped at predetermined voltages.
The amount of change &Dgr;VFM in the voltage signal VFM relative to the amount of change &Dgr;IPD in the reception current IPD is represented by the expression &Dgr;VFM=&Dgr;IPD×R
2
. The buffer circuit
22
, the bandpass filter
23
, and the main amp
24
amplify the differential voltage &Dgr;VF (&Dgr;VPF−&Dgr;VFM) of the differential output signal of the pre-amp
21
, and generate an amplified differential output signal. The comparator
25
converts the differential output signal from the main amp
24
to a digital reception signal RX.
The DC light-canceling circuit
26
cancels the direct current component (DC component) included in the reception current IPD flowing through the photodiode PD. The DC component is generated by background DC light, such as sunlight and the like, and includes a frequency component lower than the predetermined frequency band including the communication frequency. The DC light-canceling circuit
26
provides feedback for the current canceling the canceled DC component, which is included in the voltage signals VFM and VFP, to the input of the pre-amp
21
.
When light input to the photodiode PD includes light components other than communication light, the total gain of the optical receiver amps
10
and
20
is reduced, and the signal-to-noise (S/N) ratio of the optical receiver amps must be increased. Generally, an auto gain control (AGC) circuit is used as a means of reducing the gain. A more effective method of simply reducing the gain is to adjust the resistance value of the resistor R
1
(resistors R
2
and R
3
of pre-amp
21
) of the pre-amp
11
via an AGC circuit. However, when the resistance values of these resistors R
1
through R
3
are adjusted, the bias voltage fluctuates in conjunction with the variation in the resistance values. Then, a suitable bias voltage is not supplied to later-stage amps. Particularly when the optical receiver amps
10
and
20
are operated by a low voltage power supply, there is not enough margin in the bias level between amps.
When the resistance values of the resistors R
1
, R
2
, and R
3
are adjusted by an AGC circuit, the amount of attenuation (amount of change in the gain) is approximately −30 dB&OHgr;. When the optical input signal is relatively large, the gain must be reduced, which naturally requires another circuit. However, adding this circuit increases the circuit area of the optical receiver amp.
SUMMARY OF THE INVENTION
In a first aspect of the present invention, an amplification circuit for receiving an input current is provided. The amplification circuit includes a first amplifier including a current-to-voltage conversion resistor for generating a first voltage signal corresponding to the input current. A second amplifier is connected to the first amplifier to amplify the first voltage signal and generating a second voltage signal. A first gain control circuit is connected to the first and second amplifiers to generate a first gain control signal based on the second voltage signal and adjusting the resistance value of the current-to-voltage conversion resistor in accordance with the first gain control signal. A bias control circuit is connected to the first amplifier and the first gain control circuit to generate a bias control signal based on the gain control signal and adjust the bias current at the output of the first amplifier in accordance with the bias control signal.
In a second aspect of the present invention, an optical communication apparatus for receiving signal light is provided. The optical communication apparatus includes a first photoreceptor element for receiving the signal light and generating a first reception current. A first amplifier is connected to the first photoreceptor element and includes
Armstrong Kratz Quintos Hanson & Brooks, LLP
Fujitsu Limited
Nguyen Patricia
LandOfFree
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