Electrically testing an optical receiver
AssigneeXilinx, Inc.
InventorsMayank Raj, Yohan Frans, Kun-Yung Chang
Life of this patent
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Abstract
An example photodiode emulator circuit includes: a first current source circuit; first and second transistors having sources coupled together and coupled to an output of the first current source circuit, a drain of the second transistor coupled to a first node; a third transistor coupled between a drain of the first transistor and a replica load circuit; a second current source circuit coupled to the first node; a capacitor coupled between the first node and electrical ground; and a fourth transistor having a source coupled to the first node and a drain that supplies an output current.
Claims20
A photodiode emulator circuit, comprising:
- a first current source circuit;
- first and second transistors having sources coupled together and coupled to an output of the first current source circuit, a drain of the second transistor coupled to a first node;
- a third transistor coupled between a drain of the first transistor and a replica load circuit;
- a second current source circuit coupled to the first node;
- a capacitor coupled between the first node and electrical ground;
- and
- a fourth transistor having a source coupled to the first node and a drain that supplies an output current.
A test circuit in a receiver, comprising:
- a data generator configured to generate first and second logic signals that are logical complements of each other;
- and
- a photodiode emulator circuit, comprising:
- a first current source circuit;
- first and second transistors having sources coupled together and coupled to an output of the first current source circuit, wherein a drain of the second transistor is coupled to a first node, and gates of the first and second transistors receive the first and second logic signals, respectively;
- a third transistor coupled between a drain of the first transistor and a replica load circuit;
- a second current source circuit coupled to the first node;
- a capacitor coupled between the first node and electrical ground;
- and
- a fourth transistor having a source coupled to the first node and a drain that supplies an output current.
A method of emulating a photodiode at an input of a receiver, comprising:
- coupling a photodiode emulator circuit to the input of the receiver;
- driving a differential input of a differential transistor pair in the photodiode emulator circuit with differential data signals, the differential transistor pair supplying an output current to an output node coupled to the receiver;
- controlling a first current source of the photodiode emulator circuit to supply a first current to the differential transistor pair;
- controlling a second current source of the photodiode emulator circuit to supply a second current to the output node;
- and
- adjusting capacitance of a capacitor coupled between the output node and electrical ground.
Dependencies are inferred from the claim text.