Data signal threshold detection and/or recovery in optical and/or optoelectric receivers and/or transceivers
View Patent ↗Methods for receiving a signal and a detection circuit are disclosed. The detection circuit and related methods may be useful for the fast and accurate receiving of data signals. The detection circuit generally comprises a first circuit having a first time constant, a second circuit having (i) a common input with the first circuit and (ii) a second time constant, the second time constant being less than the first time constant, and a switch configured to (i) charge the first circuit with an input signal when the switch is in a first state, and (ii) charge or discharge the second circuit with the input signal when the switch is in a second state, the switch having the second state when the input signal is no longer received at the common input.
1. A method of receiving a plurality of optical signals in an optical receiver, the method comprising:
receiving a first optical signal of the plurality of optical signals with a photodiode in the optical receiver and providing a first electrical signal therefrom;
charging a first circuit in the optical receiver having a first time constant with the first electrical signal, the first electrical signal having a first common-mode voltage; and
when said first electrical signal is no longer received, charging or discharging a second circuit, said second circuit having (i) a common input and a common output with said first circuit and (ii) a second time constant substantially less than said first time constant which allows the common-mode voltage of the first electrical signal to decay to a value below an amplitude of a second electrical signal;
receiving a second optical signal of the plurality of optical signals with the photodiode and providing the second electrical signal therefrom;
prior to or simultaneously with receiving the second optical signal, selecting the first circuit to be charged by the second electrical signal;
recharging the first circuit with the second electrical signal; and
determining a decision threshold for a second electrical signal using the first circuit.
2. The method of claim 1 , wherein charging or discharging said second circuit comprises one of opening or closing a switch, and selecting the first circuit comprises the other of opening or closing the switch.
3. The method of claim 2 , wherein said switch is coupled to the common output, and charging or discharging said second circuit comprises closing said switch to decrease an impedance presented to said common input.
4. The method of claim 2 , wherein said switch is coupled to an input of said second circuit, and charging or discharging said second circuit comprises opening said switch to decrease a capacitance presented to said common input.
5. The method of claim 1 , wherein said first circuit comprises a first RC circuit, and said second circuit comprises a second RC circuit.
6. The method of claim 5 , wherein each of said first and second RC circuits comprises a first resistor and a first capacitor, and one of said first and second RC circuits comprises a third RC component.
7. The method of claim 1 , wherein charging or discharging said second circuit allows the common-mode voltage of the first electrical signal to decay, and after the common-mode voltage of the first electrical signal is allowed to decay, the first circuit is selected to be charged, the second optical signal is received, and the second electrical signal is provided.
8. An optical receiver, comprising:
a photodiode configured to receive an optical signal and provide an electrical signal;
a first circuit having a first time constant and receiving the electrical signal;
a second circuit having (i) a common input and a common output with said first circuit and (ii) a second time constant, said second time constant being substantially less than said first time constant and allowing a common-mode voltage thereon to decay or change at a faster rate than the first circuit, wherein the common-mode voltage can have a value greater than an amplitude of the electrical signal;
a switch configured to (i) charge said first circuit with the electrical signal when the switch is in a first state, and (ii) charge or discharge said second circuit when the switch is in a second state, the switch having the second state when said electrical signal is no longer received at said common input; and
logic configured to place said switch in the first state whenever said electrical signal is received at said common input for an entire duration of said electrical signal, place said switch in the second state when said electrical signal is not received at said common input, and determine a decision threshold for binary logic states of the electrical signal received by the detection circuit based on the common-mode voltage.
9. The optical receiver of claim 8 , wherein (i) said electrical signal is a single-ended signal, and (ii) each of said first and second circuits have a differential output.
10. The optical receiver of claim 9 , further comprising a differential amplifier configured to receive said differential outputs of said first and second circuits.
11. The optical receiver of claim 8 , wherein said first circuit comprises a first RC circuit, and said second circuit comprises a second RC circuit.
12. The optical receiver of claim 11 , wherein each of said first and second RC circuits comprises a first resistor and a first capacitor, and one of said first and second RC circuits comprises a third RC component.
13. The optical receiver of claim 11 , wherein said first circuit has a resistance that is substantially greater than a resistance of said second circuit.
14. The optical receiver of claim 11 , wherein said first circuit has a capacitance that is substantially greater than a capacitance of said second circuit.
15. The optical receiver of claim 8 , wherein:
said logic comprises a microcontroller or microprocessor configured to execute one or more commands to open or close said switch; and
said optical receiver further comprises a memory in electrical communication with said microcontroller or microprocessor.
16. The optical receiver of claim 15 , further comprising an amplifier configured to amplify said electrical signal.
17. The optical receiver of claim 16 , wherein said amplifier comprises a transimpedance amplifier and a gain amplifier.
18. The optical receiver of claim 15 , wherein each of said first circuit and said second circuit have a common differential output, and the optical receiver further comprises a differential amplifier having an input configured to receive said common differential output of said first circuit and said second circuit.
19. The optical receiver of claim 15 , wherein said microprocessor or microcontroller is further configured to execute one or more commands configured to recharge said first circuit when said electrical signal is received again at said common input.
20. The optical receiver of claim 8 , wherein said logic is configured to place said switch in the second state and allow the common-mode voltage of the electrical signal to decay, then after the common-mode voltage of the electrical signal is allowed to decay to a value less than an amplitude of a successive electrical signal, place said switch in the first state.