Noise discriminator for enhanced noise detection in a passive optical network burst mode receiver
View Patent ↗A noise discriminator circuit and a noise discrimination method in a burst mode receiver is configured to determine the validity of an incoming burst signal by analyzing the timing of the signal edges of incoming signal to look for a time duration conforming to the preamble data bits of a valid burst signal. In one embodiment, the noise discriminator circuit and method analyze the time duration between signal edges of the same pulse of an incoming signal. In another embodiment, the noise discriminator circuit and method analyze the time duration between a first set of pulses of an incoming signal and the time duration between signal edges of a second set of pulses of the incoming signal. When the time durations are within a given time range relating to a predetermined timing separation of a valid burst signal, the incoming signal is validated as a valid burst signal.
1. A method in a burst mode receiver to determine the validity of an incoming burst signal, comprising:
receiving consecutive pulses of an incoming signal;
determining if a first time duration between a signal edge of a first pulse and a signal edge of a second pulse is within a first time range of a predetermined timing separation of a valid burst signal, the first pulse and the second pulse being consecutive pulses;
if the first time duration is within the first time range, determining if a second time duration between the signal edge of the second pulse and a signal edge of a third pulse is within the first time range, the second pulse and the third pulse being consecutive pulses;
if the second time duration is within the first time range, asserting a signal indicative of a valid burst signal; and
if the first time duration is not within the first time range or the second time duration is not within the first time range, deasserting the signal indicative of a valid burst signal.
2. The method of claim 1 , wherein asserting a signal indicative of a valid burst signal comprises asserting a signal detect signal.
3. The method of claim 2 , wherein asserting a signal detect signal comprises asserting the signal detect signal on the signal edge of the third pulse when the signal indicative of a valid burst signal is asserted.
4. The method of claim 1 , wherein after deasserting the signal indicative of a valid burst signal, the method further comprises discarding at least the first and second pulses and returning to receiving the next three consecutive pulses.
5. The method of claim 1 , wherein the predetermined timing separation of a valid burst signal comprises the predetermined timing separation of the signal edges in the preamble data bits of the burst signal.
6. The method of claim 5 , wherein the first time range comprises a time range around twice the period of the data rate of the incoming burst signal.
7. The method of claim 1 , further comprises:
when the first time duration is shorter than the first time range, discarding the first pulse and returning to receive the next consecutive pulses, the second pulse being used as the first pulse.
8. The method of claim 1 , further comprises:
when the first time duration is longer than the first time range, discarding the first and second pulses, asserting a reset signal and returning to receive the next consecutive pulses.
9. The method of claim 1 , further comprises:
when the second time duration is shorter than the first time range, discarding the second pulse and returning to receive the next consecutive pulses, the third pulse being used as the first pulse.
10. The method of claim 1 , further comprises:
when the second time duration is longer than the first time range, discarding the first, second and third pulses, asserting a reset signal and returning to receive the next consecutive pulses.
11. The method of claim 1 , wherein the signal edges comprise rising edges, falling edges, or a combination of rising and falling edges.
12. A limiting amplifier for a burst mode receiver, comprising:
an amplifier configured to receive and amplify an input signal representative of an incoming burst signal;
a buffer configured to receive the amplified input signal and to generate an output signal;
a noise discriminator circuit configured to receive the amplified input signal and to assert a valid output signal when a first time duration between a signal edge of a first pulse and a signal edge of a second pulse is within a first time range of a predetermined timing separation of a valid burst signal, the first pulse and the second pulse being consecutive pulses, and when a second time duration between the signal edge of the second pulse and a signal edge of a third pulse is within the first time range, the second pulse and the third pulse being consecutive pulses; and
a signal detect generator circuit configured to assert a signal detect signal when the valid output signal is asserted.
13. The limiting amplifier of claim 12 , further comprising:
a signal level detector circuit configured to receive the amplified input signal and to generate a detected data signal when the amplified input signal has a signal amplitude greater than a signal threshold,
wherein the signal detect generator circuit is configured to assert the signal detect signal when both the detected data signal is asserted and the valid output signal is asserted.
14. The limiting amplifier of claim 13 , wherein the noise discriminator circuit is configured to receive either the amplified input signal or the detected data signal and to assert the valid output signal when both the first time duration and the second time duration are within the time range of a predetermined timing separation of a valid burst signal.
15. The limiting amplifier of claim 12 , wherein the signal detect generator circuit is configured to deassert the signal detect signal when the first time duration or the second time duration is not within the first time range, the noise discriminator circuit further configured to discard at least the first and second pulses and return to receiving the next three consecutive pulses.
16. The limiting amplifier of claim 12 , wherein when the first time duration is shorter than the first time range, the noise discriminator circuit is configured to discard the first pulse and to receive the next consecutive pulses, the second pulse being used as the first pulse.
17. The limiting amplifier of claim 12 , wherein when the first time duration is longer than the first time range, the noise discriminator circuit is configured to discard the first and second pulses and to assert a reset signal and return to receive the next consecutive pulses.
18. The limiting amplifier of claim 12 , wherein when the second time duration is shorter than the first time range, the noise discriminator circuit is configured to discard the second pulse and return to receive the next consecutive pulses, the third pulse being used as the first pulse.
19. The limiting amplifier of claim 12 , wherein when the second time duration is longer than the first time range, the noise discriminator circuit is configured to discard the first, second and third pulses, assert a reset signal and return to receive the next consecutive pulses.
20. The limiting amplifier of claim 12 , wherein the predetermined timing separation of a valid burst signal comprises the predetermined timing separation of the signal edges in the preamble data bits of the burst signal.
21. The limiting amplifier of claim 20 , wherein the predetermined timing separation of the signal edges in the preamble data bits of the burst signal comprises a timing separation being twice the period of the data rate of the burst signal.
22. The limiting amplifier of claim 12 , wherein the signal edges of the pulses comprise rising edges, falling edges, or a combination of rising and falling edges.