Discrete bootstrapping in an optical receiver to prevent signal feedback
View Patent ↗An optical receiver assembly that is configured to avoid the introduction of feedback in an electrical signal converted by the assembly is disclosed. In one embodiment, an optical receiver assembly is disclosed, comprising a capacitor, an optical detector provided with a power supply being mounted on a top electrode of the capacitor, and an amplifier mounted on the reference surface. The assembly further includes an isolator interposed between the reference surface and the capacitor, wherein the isolator includes a bottom layer of dielectric material that is affixed to a portion of the reference surface, and a metallic top plate that is electrically coupled both to a ground of the amplifier and to the capacitor. This configuration bootstraps the amplifier ground to the amplifier input via the photodiode top electrode of the capacitor to cancel out feedback signals present at the amplifier ground.
1. A feedback controlling optical receiver assembly, comprising:
a reference surface;
a capacitor;
an optical detector mounted on the capacitor, a top electrode of the capacitor being electrically coupled to a bottom electrode of the optical detector;
an amplifier mounted on the reference surface, the amplifier receiving and amplifying an electrical signal produced by the optical detector; and
an isolator mounted on the reference surface such that the isolator is interposed between the reference surface and the capacitor, the isolator configured to electrically couple a feedback signal present at a ground of the amplifier to an input of the amplifier independent of the reference surface such that most of the feedback signal is cancelled, wherein the isolator includes:
a bottom layer of dielectric material that is affixed to a portion of the reference surface;
a metallic top plate, the top plate being electrically coupled both to a ground of the amplifier and to a bottom electrode of the capacitor; and
two wires extending from the amplifier to the metallic top plate, the wires being arranged in a non-parallel configuration to prevent mutual coupling.
2. The optical receiver assembly as defined in claim 1 , wherein the isolator permits the feedback signal present at the ground of the amplifier to be transmitted to the optical detector and from the optical detector to the input of the amplifier.
3. The optical receiver assembly as defined in claim 1 , wherein the optical detector is an avalanche photodiode.
4. The optical receiver assembly as defined in claim 1 , wherein the reference surface is a grounded surface of a base of an optical receiver package.
5. The optical receiver assembly as defined in claim 4 , wherein the isolator capacitively isolates the optical detector from the grounded reference surface.
6. The optical receiver assembly as defined in claim 1 , wherein the isolator reduces parasitic capacitance and parasitic inductance in the optical receiver assembly.
7. The optical receiver assembly as defined in claim 1 , wherein the isolator is further configured to permit the feedback signal to be transmitted from the optical detector to the input of the amplifier such that at least a portion of the feedback is substantially cancelled from the optical receiver assembly.
8. The optical receiver assembly as defined in claim 1 , wherein the bottom layer of dielectric material is composed of a low dielectric material having a dielectric constant of less than 10.
9. The optical receiver assembly as defined in claim 1 , wherein the bottom layer of dielectric material is composed of aluminum oxide, fused silica, or aluminum nitride.
10. The optical receiver assembly as defined in claim 1 , wherein the metallic top plate comprises gold.
11. A receiver optical subassembly comprising:
a hermetically sealed package including a grounded base;
a plurality of electrical leads that extend through the base in order to provide electrical communication between package components and devices positioned exterior to the package; and
the optical receiver assembly as defined in claim 1 positioned within the hermetically sealed package, the grounded base defining the reference surface of the optical receiver assembly.
12. The receiver optical subassembly as defined in claim 11 , wherein the amplifier comprises a transimpedance amplifier.
13. The receiver optical subassembly as defined in claim 12 , wherein the isolator enables an electrical path to be established between the ground of the transimpedance amplifier and the input of the transimpedance amplifier via the metallic layer, the first capacitor, and the photodiode.
14. The receiver optical subassembly as defined in claim 13 , wherein the electrical path provides a conduit by which feedback signals present at the ground of the transimpedance amplifier are transmitted to the input of the transimpedance amplifier to cancel at least a portion of the feedback signal.
15. The receiver optical subassembly as defined in claim 14 , wherein the electrical path is independent of the grounded reference surface.
16. The receiver optical subassembly as defined in claim 11 , wherein a power supply for the photodiode is provided by a lead of the base and is supplied to a first electrode of the capacitor, wherein a decoupling capacitor is interposed between the lead and the capacitor.
17. An optical transceiver module, comprising:
a housing;
a printed circuit board at least partially included in the housing;
a transmitter optical subassembly electrically coupled to the printed circuit board; and
the receiver optical subassembly as defined in claim 11 electrically coupled to the printed circuit board.
18. The optical transceiver module as defined in claim 17 , wherein the metallic layer of the isolator is electrically coupled to the ground of the amplifier by one of the two wires that extends from a bond pad of the amplifier to the metallic layer.
19. The optical transceiver module as defined in claim 17 , wherein a power supply is supplied to the optical detector via a first electrode of the capacitor.
20. A feedback controlling optical receiver assembly, comprising:
a reference surface;
a capacitor;
an optical detector mounted on the capacitor, a top electrode of the capacitor being electrically coupled to a bottom electrode of the optical detector;
an amplifier mounted on the reference surface, the amplifier receiving and amplifying an electrical signal produced by the optical detector; and
an isolator mounted on the reference surface such that the isolator is interposed between the reference surface and the capacitor, the isolator configured to electrically couple a feedback signal present at a ground of the amplifier to an input of the amplifier independent of the reference surface such that most of the feedback signal is cancelled, wherein the isolator includes:
a bottom layer of dielectric material that is affixed to a portion of the reference surface; and
a metallic top plate, the top plate being electrically coupled both to a ground of the amplifier and to a bottom electrode of the capacitor.