Variable gain optical modulator with open collector driver amplifier and method of operation
A distributed amplifier system comprising an impedance matching network configured to match an input impedance to an output impedance of the signal source, and a DC block configured to block DC components in the input signal. A variable gain amplifier adjusts the gain applied to the input signal based on a gain control signal to generate a gain adjusted signal. An emitter follower circuit receives and processes the gain adjusted signal to introduce gain peaking to create a modified signal. A distributed amplifier receives and amplifies the modified signal from the emitter follower circuit, to create an amplified signal. The distributed amplifier includes a termination network and one or more impedance matching elements configured for gain shaping the amplified signal. The gain peaking introduced by the emitter follower circuit is controlled by a variable current source. The distributed amplifier may be an open collector distributed amplifier.
1 . A distributed driver for an optic signal generator comprising:
a driver input configured to receive an input signal;
a driver output configured to provide an amplified output signal to the optic signal generator or modulator;
a first amplifier cell comprising a first amplifier cell input, one or more amplifiers, and a first amplifier cell output, the first amplifier cell configured to receive and amplify the input signal to create a first amplified signal on the first amplifier cell output;
a second amplifier cell comprising a second amplifier cell input, one or more amplifiers, and a second amplifier cell output, the second amplifier cell configured to receive and amplify the input signal to create a second amplified signal on the second amplifier cell output;
a first conductive path having a first end and a second end, the first end connected to the driver input, such that the first conductive path connects the driver input to the first amplifier cell input and the second amplifier cell input, to thereby carry the input signal to the first amplifier cell and the second amplifier cell, such that one or more inductances in first conductive path counteracts a capacitance associated with the first amplifier cell and the second amplifier cell;
a gain shaping termination network, connected to or part of, the second end of the first conductive path, configured to perform frequency specific gain shaping; and
a second conductive path such that the second conductive path connects the driver output to the first amplifier cell output and the second amplifier cell output, to thereby carry the amplified output signal created by the first amplifier cell and the second amplifier cell to the driver output, such that one or more inductances in second conductive path counteracts a capacitance associated with the first amplifier cell and the second amplifier cell.
2 . The distributed driver of claim 1 wherein the one or more amplifiers are configured as a cascode differential pair.
3 . The distributed driver of claim 1 further comprising additional amplifier cells having the same configuration as the first and second amplifier cells.
4 . The distributed driver of claim 1 wherein the first amplifier cell and the second amplifier cells have an open collector configuration.
5 . The distributed driver of claim 1 further comprising:
one or more emitter follower circuits connected between the first conductive path and the first amplifier cell input; and
one or more emitter follower circuits connected between the first conductive path and the second amplifier cell input.
6 . The distributed driver of claim 5 further comprising one or more variable current sources, within each emitter follower circuit, configured to control a frequency specific gain adjustment performed by the one or more emitter follower circuits.
7 . The distributed driver of claim 1 wherein the gain shaping termination network comprises one or more inductors and one or more resistors.
8 . The distributed driver of claim 1 wherein the gain shaping termination network comprises one or more inductors, one or more resistors, and one or more capacitors connected in series between a ground and an inductor in the input path.
9 . A method for amplifying, with a distributed amplifier, an input signal, the method comprising:
receiving the input signal on an input path, the input path having a first end and a second end, such that the first end receives the input signal, and the second end is terminated with a gain shaping termination network, wherein the input path further comprises one or more inductors;
distributing the input signal to two or more amplifier cells through the input path that has one or more inductors and a termination network, wherein distributing includes;
introducing frequency specific gain shaping into the input signal with the gain shaping termination network;
canceling parasitic capacitance associated with two or more amplifiers, in the distributed amplifier, with the one or more inductors;
amplifying the input signal after frequency specific gain adjustment with the two or more amplifier cells to generate amplified output signals;
combining the amplified output signals from the two or more amplifier cells on an output path as a combined output signal, the output path having one or more inductors that cancel output parasitic capacitance of the two or more amplifier cells; and
presenting the combined output signal on an output from the distributed amplifier, the output connected to the output path.
10 . The method of claim 9 wherein the gain shaping termination network consists of one or more resistors, one or more inductors and one or more capacitors, and the gain shaping termination network is located at an end of the input path that is opposite an end of the input path that receives the input signal.
11 . The method of claim 9 wherein an inductor from the input path and an inductor from the output path is associated with each amplifier cell, and the inductors are realized as integrated transmission line elements.
12 . The method of claim 9 wherein the gain shaping termination network comprises series connected inductors, resistors, and capacitors, which connect to an inductor in the input path.
13 . The method of claim 9 wherein the two or more amplifier cells are configured in an open collector configuration.
14 . The method of claim 9 further comprising performing additional frequency specific gain adjustment with one or more emitter follower circuits in at least one of the two or more amplifier cells.
15 . The distributed driver of claim 9 further comprising providing a control signal to a variable current source that is part of the at least one emitter follower circuit, such that the control signal determines the amount of frequency specific gain adjustment introduced by the at least one emitter follower circuit.
16 . The method of claim 9 wherein the distributed amplifier is configured to accept and amplify a differential signal and the input signal is a differential signal.
17 . A distributed amplifier for an optic signal generator comprising:
two or more amplifier cells, each cell having:
two or more amplifiers comprising cascode connected transistors configured to amplify a received signal to then create an amplified signal;
an output path configured to carry the amplified signal;
an input path, having a first end and a second end, configured to receive the input signal at the first end and distribute the input signal to the two or more amplifier cells, the input path including one or more inductors that cancel parasitic capacitance from the two or more amplifier cells;
an output path connected to the amplifier cell output of the two or more amplifier cells to receive and output the amplified signal from two or more amplifier cells, the output path including one or more inductors that cancel parasitic capacitance from the two or more amplifier cells; and
a gain shaping network at the second end of the input path, the gain shaping network configured to introduce frequency specific gain shaping in the amplified signal from two or more amplifier cells.
18 . The distributed driver of claim 17 wherein an inductor from the input path and an inductor from the output path is associated with each amplifier cell.
19 . The distributed driver of claim 17 wherein the gain shaping network comprises series connected inductors, resistors, and capacitors, which connect to an inductor in the input path.
20 . The distributed amplifier of claim 17 wherein the distributed amplifier is configured to amplify a differential signal, the input path comprises a first input path and a second input path, and the first input path and the second input path connect through one or more resistor at the second end.