Electric power conversion systems – Current conversion – Constant current to constant voltage or vice versa
Reexamination Certificate
2002-02-21
2003-01-07
Vu, Bao Q. (Department: 2838)
Electric power conversion systems
Current conversion
Constant current to constant voltage or vice versa
C323S315000, C323S316000
Reexamination Certificate
active
06504736
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a current-voltage converter that converts presence/absence of an input signal into a voltage signal when current wide in amplitude range is inputted. More particularly, it relates to a current-voltage converter used for the case after an optical input signal detected by an optical detective element in the course optical communications or the like is converted into a current input signal.
2. Description of Related Art
Recent years, infrared data communication (IrDA communication) function for connecting communication terminals with infrared rays has been applied to mobile terminals, personal computers, cellular phones, and the like. Furthermore, optical fiber communication networks have been well established as communication infrastructure. In such a communication system, an optical signal of infrared ray or the like is used as a digital signal. More specifically, an optical signal is converted into a current signal and the converted current signal is further converted into a voltage signal, thereby making it possible to detect presence/absence of the optical signal.
FIG. 13
shows a current-voltage converter
100
as a first related art. A pair of constant current source transistors M
101
, and M
102
connect emitter terminals of transistors Q
101
and Q
102
and ground voltage GND. Base terminals of the transistor Q
101
, and Q
102
connect to bias voltage source VBIAS. Diodes D
101
and D
102
connect collector terminals of the transistors Q
101
and Q
102
and power source voltage VCC. A photo diode PD for detecting an optical input signal connects to a connection point of the emitter terminal of the transistor Q
101
and the constant current source transistor M
101
. Further on, connection points VM and VP connect the transistor Q
101
and the diode D
101
, the transistor Q
102
and the diode D
102
, respectively. These connection points VM and VP connect to a pair of differential input terminals of a differential amplifier circuit AMP
101
to constitute a conversion voltage terminal VM and a reference voltage terminal VP for the current-voltage converter
100
.
An optical input signal is detected by the photo diode PD, i.e., inputted as a current input signal Iin, and then, converted into a voltage value, and finally outputted to a next stage such as the differential amplifier circuit AMP
101
. It should be noted that the input terminal of the current-voltage converter
100
herein is shown as a single input. That is, as a circuit structure to conduct current-voltage conversion of an input signal Iin, the current-voltage converter
100
is provided with the diode D
101
, the transistor Q
101
, and the constant current source transistor M
101
. A similar circuit structure consisting of the diode D
102
, the transistor Q
102
, and the constant current source transistor M
102
is also incorporated therein so as to determine an operational point of the current-voltage converter
100
. Thereby, it is structured such that differential voltage between reference voltage VP corresponding to output voltage to be outputted to the reference voltage terminal VP and conversion voltage VM to be outputted to conversion voltage terminal VM is outputted as output voltage. Furthermore, as to the complimentary circuit, the connection point for the emitter terminal of the transistor Q
102
and the constant current source transistor M
102
can connect to a load such as a capacitance element. More specifically, the capacitance element is structured as a dummy terminal for making input loads of differential inputs same and corresponds to a the photo diode PD. Furthermore, a pair of current input signals complementary to each other can be inputted to obtain differential current signals.
Current converted into a current input signal Iin by the photo diode PD joins to a bias current IB
1
flowing from the constant current source transistor M
101
and flows to the diode D
101
through the transistor Q
101
. An anode terminal of the diode D
101
connects to the power source voltage terminal VCC. Therefore, forward voltage of the diode D
101
having dropped is outputted to the conversion voltage terminal VM. The forward voltage of the diode D
101
generates when the converted current flows there. On the other hand, a bias current IB
2
flows coming from the constant current source transistor M
102
flows into the diode D
102
and dropping voltage equivalent to the forward voltage of the diode D
102
obtained when the bias current IB
2
from the power source voltage VCC flows thereto. Accordingly, the differential amplifier circuit AMP
101
detects two inputs as differential voltage, namely, (1) the reference voltage VP outputted from the reference voltage terminal VP, and (2) the conversion voltage VM outputted from the conversion voltage terminal VM equivalent to voltage having dropped by the forward voltage which generates when a current input signal Iin flows to the diode D
101
in comparison with the reference voltage VP.
In the current-voltage converter
100
, the diode D
101
converts a current input signal Iin into a form of logarithmic compression. Therefore, the conversion voltage VM for the conversion voltage terminal VM operates with an amplitude approximate to an operational point of about 0.7 V corresponding to forward voltage which makes diode conductive.
In general, a group of the diode D
101
, the transistor Q
101
, and the constant current source transistor M
101
, and a corresponding group of the diode D
102
, the transistor Q
102
, and the constant current source transistor M
102
are structured with identical circuit elements, respectively. Theirs respective bias currents IB
1
and IB
2
are identical to each other.
FIG. 14
shows a current-voltage converter
200
as a second related art. In addition to the component elements of the current-voltage converter
100
, the current-voltage converter
200
has a structure such that resistance elements R
101
and R
102
are connected in parallel to diodes D
101
and D
102
connected between collector terminals of transistors Q
101
and Q
102
, and power source voltage VCC. Other than the above-mentioned partial structure, an essential circuit structure of the current-voltage converter
200
is similar to that of the current-voltage converter
100
. Accordingly, in the second related art, same numerals are assigned to composing elements identical to the first related art and description of them will be omitted.
In the current-voltage converter
200
, bias currents IB
1
and IB
2
flow to loads R
101
-D
101
and R
102
-D
102
, respectively, wherein the resistance elements R
101
, R
102
and the diodes D
101
, D
102
are connected in parallel to one another. Accordingly, as to the load to which a current input signal Iin flows, current IB
1
+Iin mainly flows in the resistance element R
1
until terminal-to-terminal voltage drop of a load reaches of about 0.7 V, forward voltage which makes the diode D
101
conductive. A characteristic of conversion voltage outputted from a conversion voltage terminal VM varies in proportion to a current input signal Iin. After the current increases and the terminal-to-terminal voltage drop of a load reaches of about 0.7 V, the forward voltage of the diode D
101
, the current mainly flows in the diode D
101
and the characteristic of the conversion voltage outputted from the conversion voltage terminal VM shifts to a characteristic of logarithmic compression against the current input signal Iin.
In general, a group of the diode D
101
, the transistor Q
101
, and the constant current source transistor M
101
, and a corresponding group of the diode D
102
, the transistor Q
102
, and the constant current source transistor M
102
are structured with identical circuit elements, respectively. Theirs respective bias currents IB
1
and IB
2
are identical to each other. Further on, theirs respective resistance elements are also identical to each other.
However, in optical communications such as IrDA communication including inf
Staas & Halsey , LLP
Vu Bao Q.
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