Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-08-02
2001-07-17
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S2140LA
Reexamination Certificate
active
06262411
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to photodetector receivers and more particularly to a photodetector receiver which obviates the need for linear amplification.
BACKGROUND OF THE INVENTION
A prior art direct detector, is shown by way of example in
FIG. 1. A
direct detector detects the signal from variations in the signal amplitude, as opposed to variations in frequency. As shown, a light wave is incident at a photodetector
10
, shown for purposes of illustration as a photodiode. The resulting electrical current output from detector
10
may pass through a pre-amplifier
20
such as shown, typically used to amplify the electrical signal to an intermediate level without degrading the signal to noise ratio of the signal. Thereafter, the signal is further amplified as it passes through post amplifier
30
for large amplification of the voltage for input to decision circuit
40
. At this point the voltage is split along two paths. One path leads to a decision circuit
40
for data recovery, while the other path leads to a clock recovery device
50
for correcting the timing of the data signal which may have become distorted during transmission. The clock is split at power splitter
60
in order to provide timing information to decision circuit
40
and for external use.
The amplification stage after detection is necessary because the incident signal may be at a low power level on the order of 50 microwatts or lower, which will generate a low voltage on the order of 15 millivolts. The logic circuit, however, typically requires 1 volt peak to peak. The drawback of the device of
FIG. 1
is that it includes electrical connections and devices. The electrical components are sensitive to data transmission rates and should have sufficient electrical bandwidth to operate at the data transmission rate. As bit rates increase, obtaining amplifiers with the proper bandwidth becomes a challenge. While connections can be fabricated to accept the higher bit rates, such as in the range of gigabits, they must also be compatible with the amplifiers they inter-connect which traditionally have impedance ratings of 50 ohms. Accordingly, in light of ever increasing demand for higher data transfer rates, it is desirable to reduce the constraints created by the electrical elements in the circuit, e.g. transistors, capacitors and wiring.
SUMMARY OF THE INVENTION
Accordingly, the present invention is a direct detection device in which photodetectors and resistors replace all linear amplifiers. An optically amplified light wave is split along two paths: a clock recovery path and a data path. The light along the clock recovery path is detected by a first photodetector in series with a resistor R
1
where the resistance of R
1
is selected so as to provide a desired voltage at the circuit node common to the detector R
1
and the clock recovery device. The output from the clock recovery device is power split with one half being used to clock the decision circuit and the other half available for external use.
The light along the data path is also split a second time with each resulting path leading to a photodetector in series with a resistor, R
2
and R
3
, respectively. Each of these photodetectors lead to an input in the decision circuit. One of the inputs to the decision circuit being the data and the other being an average DC voltage of the data signal. Each of the photodetectors is advantageously a p-i-n detector. It is also advantageous to fabricate a single chip to include the three photodetectors, their respective resistors, the clock recovery device and the decision circuit.
REFERENCES:
patent: 5892220 (1999-04-01), Woodward
Agere Systems Optoelectronics Guardian Corp.
Le Que T.
LandOfFree
Direct detection receiver does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Direct detection receiver, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Direct detection receiver will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2509071