Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
2000-08-22
2003-01-07
Pyo, Kevin (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S2140LS, C359S199200
Reexamination Certificate
active
06504140
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical interconnection receiving module. The present invention particularly relates to a technology for preventing the effect of cross talk noise caused by an amplifier of another channel in a photoelectric conversion circuit dealing with a plurality of channel signals and an optical interconnection receiving module including the photoelectric conversion circuit. The optical interconnection receiving module according to the present invention is used in an optical communication system, and is useful in converting an optical signal into an electric signal and in amplifying and distinguishing the electric signal.
2. Related Arts
Conventionally, as shown in
FIG. 1
, at an apparatus on the transmitting side in an optical communication system, information to be transmitted is converted from an electric signal to an optical signal by a transmission module
100
having a laser diode array
120
and the like, and the information is transmitted to an apparatus on the receiving side via an optical fiber array
200
. At the apparatus on the receiving side, the optical signal received by an optical interconnection receiving module
300
having a photodiode array
320
and the like is converted to an electric signal and sent to an interface circuit of a microcomputer system and the like.
FIG. 9
shows a basic configuration of an input distinguishing circuit IDC provided on the input terminal side of a receiving IC (semiconductor integrated circuit) in the optical interconnection receiving module
300
. In the input distinguishing circuit shown in the figure, an electric signal converted from an optical signal by a photodiode
321
is amplified at a preamplifier
331
and supplied to a comparator
332
. At the comparator
332
, the signal is compared with reference voltage Vref to be distinguished as or “1”. Also, an amplifier
333
having the same type of circuit as that of the preamplifier
331
is used as a circuit for generating the reference voltage Vref. This makes it possible to provide high resistance to power supply noise.
It is possible to provide high resistance to power, supply noise for the following reason. If the amplifier
333
for generating the reference voltage Vref has the same type of circuit as that of the preamplifier
331
, the noises accompanying the two inputs from the two amplifiers to the comparator
332
are in phase with each other. Therefore, the effect of supply voltage noise will not appear in the output of the.comparator
332
. Specifically, in the case where the reference amplifier
333
has the same type of circuit as that of the preamplifier
331
, even if noise appears in the output of the preamplifier
331
due to the effect of the noise carried with the supply voltage Vcc, the same noise also appears in the output of the reference amplifier
333
, which is supplied with the common supply voltage Vcc. Therefore, the relative correlation between the two inputs of the comparator
332
is not changed, that is, the noises accompanying the two inputs from the two amplifiers to the comparator
332
are in phase with each other. Thus, no effect of, supply voltage noise will appear in the output of the comparator
332
.
However, in the circuit shown in
FIG. 9
, the input terminal of the preamplifier
331
is connected with the photodiode
321
, while the input terminal of the reference amplifier
333
is not connected with the photodiode
321
. Therefore, the circuit shown in
FIG. 9
is not perfectly symmetrical. Thus, it is equivalent to the fact that a capacitance is connected between the input terminal of the preamplifier
331
and the supply voltage terminal Vcc, and no capacitance is connected to the input terminal of the reference amplifier
333
. Therefore, power supply noise comes into the input terminal of the preamplifier
331
via the photodiode
321
, while such supply voltage noise does not come into the input terminal of the reference amplifier
333
. Specifically, in terms of alternating current, the input frequency response characteristic of the preamplifier
331
and the input frequency response characteristic of the reference amplifier
333
with respect to power supply noise differ from each other, as shown in FIG.
10
A. In the figure, a dotted line denotes the frequency characteristics of the output of the preamplifier, while a solid line denotes the frequency characteristics of the output of the reference amplifier. Thus, in the circuit shown in
FIG. 9
, the response to cross talk noise caused by the input distinguishing circuit of another channel differs between the preamplifier
331
and the reference amplifier
333
. As a result, as the cross talk noise is increased, the noise that has come into the preamplifier
331
might cause the output of the preamplifier
331
to exceed the reference voltage Vref supplied from the reference amplifier
333
, and the comparator
332
might wrongly distinguish the signal.
It is desirable especially in a module that receives a plurality of channel signals to have a receiving semiconductor integrated circuit that can deal with a wide range of input signals, including a small input signal that causes a current of a few &mgr;A to flow through the photodiode as well as a large input signal that causes a current of a few mA to flow through the photodiode. However, on a channel where a large signal comes in, a current of a few mA flows through the bonding wire that connects the power supply terminal and the photodiode, and therefore a relatively large noise occurs in the supply voltage due to the inductance component of the bonding wire. The circuit needs to be designed in such a way that it can correctly distinguish signals even when the noise mentioned above comes through a power supply line into the preamplifier and the reference amplifier of a channel where only a current of a few &mgr;A flows.
Incidentally, regarding a module for photoelectric conversion, there is proposed an invention according to which a capacitance equivalent to that of the photodiode is connected between the input terminal of a dummy amplifier and the supply voltage terminal, so that the effect of noise attributed to variations in power supply and temperature can be cancelled out by the preamplifier side and the dummy amplifier side. An example of this is found in, for example, Japanese Patent Laid-open No. Hei
8-139342
. Incidentally, the dummy amplifier mentioned above corresponds to the reference amplifier according to the present invention. The invention mentioned above is similar to the present invention in that the effect of noise is cancelled out, but it does not take into consideration a module that receives multi-channel signals. Thus, the embodiments of the above invention were not sufficient in terms of the prevention of the effect of cross talk noise produced from a channel where a large current of a few mA flows to a channel where only a small current of a few &mgr;A flows. Moreover, according to the prior invention mentioned above, a discrete capacitor is used as equivalent capacitance connected to the input terminal of the dummy amplifier, and therefore the above invention has the disadvantage of increasing the size of the module. The resulting size of a multi-channel module, in particular, may be fatally large for a product.
An object of the present invention is to provide an optical interconnection receiving module that can accurately distinguish an input signal by canceling out the effect of cross talk noise caused by the input signal of another channel on the preamplifier side and the reference amplifier side.
Another object of the present invention is to provide suitable device structures for a bypass capacitor used to stabilize supply voltage and for a capacitance device used to cancel out the effect of cross talk noise caused by the input signal of another channel on the preamplifier side and on the reference amplifier side, and thus reduce the size of the optical interconnection receiving module.
The above and oth
Harada Takashi
Hayashi Kiyoshi
Shiramizu Nobuhiro
Ueno Satoshi
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Pyo Kevin
Sohn Seung C.
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