Linear amplifier for use with laser driver signal
View Patent ↗An active linear amplifier circuit mounted in an optoelectronic package includes input nodes for receiving a differential signal pair, a first bipolar transistor, a second bipolar transistor, an electro-optical transducer and a decoupling circuit. A base terminal of the first bipolar transistor is coupled to the two input nodes and an emitter terminal of the first bipolar transistor is coupled to a base terminal of the second bipolar transistor. A collector terminal of the first bipolar transistor is coupled to a first terminal of the electro-optical transducer, the first terminal of the electro-optical transducer also being configured to be coupled to a voltage source. A collector terminal of the second bipolar transistor is coupled to a second terminal of the electro-optical transducer and an emitter terminal of the second bipolar transistor is coupled to a signal ground which is not the header ground.
1. An active linear transmitter optical subassembly, comprising:
a header electrically coupled to a chassis ground; and
a circuit mounted on the header and comprising:
a first input node configured to receive a first data signal;
a second input node configured to receive a second data signal that is complementary of the first data signal;
a buffer stage having a first node coupled to the first input node and the buffer stage having a second node coupled to the second input node, the buffer stage including two termination resistors, a capacitor and a first bipolar transistor;
an amplifier stage having a fifth node coupled to a third node of the buffer stage, the third node of the buffer stage including an emitter terminal of the first bipolar transistor, and the amplifier stage having a sixth node coupled to a signal ground, wherein the signal ground is not coupled to the chassis ground; and
an electro-optical transducer having an eighth node coupled to a seventh node of the amplifier stage and the electro-optical transducer having a ninth node configured to be coupled to a voltage source, the electro-optical transducer being coupled to a fourth node of the buffer stage, the fourth node of the buffer stage including a collector terminal of the first bipolar transistor.
2. The transmitter optical subassembly of claim 1 , wherein the first input node and the second input node include AC-coupling capacitors.
3. The transmitter optical subassembly of claim 1 , wherein:
the amplifier stage includes a second bipolar transistor;
the fifth node of the amplifier stage includes a base terminal of the second bipolar transistor;
the sixth node of the amplifier stage includes an emitter terminal of the second bipolar transistor; and
the seventh node of the amplifier stage includes a collector terminal of the second bipolar transistor.
4. The transmitter optical subassembly of claim 1 , wherein the signal ground is not a radio frequency (“RF”) ground.
5. The transmitter optical subassembly of claim 1 , wherein the first and second data signals are received from a laser driver over a differential transmission line.
6. The transmitter optical subassembly of claim 5 , wherein the laser driver performs waveform shaping on the first and second data signals prior to providing the first and second data signals to the first and second input nodes.
7. The transmitter optical subassembly of claim 6 , wherein the buffer stage converts the first and second data signals into a single-ended signal and provides the single-ended signal to the amplifier stage.
8. The transmitter optical subassembly of claim 7 , wherein the amplifier stage linearly amplifies the single-ended signal, thereby preserving the waveform shaping performed by the laser driver.
9. The transmitter optical subassembly of claim 1 , wherein the electro-optical transducer is a distributed feedback laser.
10. The active linear transmitter optical subassembly of claim 1 , wherein the impedance at each of the first and second nodes of the buffer stage is substantially greater than the impedance at the third node of the buffer stage.
11. The active linear transmitter optical subassembly of claim 1 , wherein the impedance at each of the first and second nodes of the buffer stage is about 50 ohms, and the impedance at the third node of the buffer stage is less than 5 ohms.
12. The active linear transmitter optical subassembly of claim 1 , further comprising a Current Mode Logic (CML) output stage coupled to the first and second input nodes.
13. An optical transceiver module including the active linear transmitter optical subassembly according to claim 1 , and further comprising:
a printed circuit board to which the active linear transmitter optical subassembly of claim 1 is coupled, and the printed circuit board including an edge connector;
a receiver optical subassembly (ROSA) coupled to the printed circuit board; and
a housing within which the active linear transmitter optical subassembly of claim 1 and the receiver optical subassembly are partially received.
14. The optical transceiver module of claim 13 , wherein the chassis ground to which the header is coupled comprises a chassis ground of the optical transceiver module.
15. The active linear transmitter optical subassembly according to claim 1 , further comprising a differential input connected to the buffer stage, the buffer stage isolating the amplifier stage from the differential input.
16. The active linear transmitter optical subassembly according to claim 1 , further comprising a decoupling circuit having first and second terminals, the first terminal of the decoupling circuit being coupled to the ninth node of the electro-optical transducer and to the collector terminal of the first bipolar transistor, and the second terminal of the decoupling circuit being coupled to the signal ground.
17. The optical transceiver module according to claim 13 , wherein an electromagnetic interference (EMI) loop of the active optical transceiver module is defined entirely within the active linear transmitter optical subassembly.