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 amplifier with variable gain control stage comprising:
a variable gain amplifier comprising:
a signal input configured to receive a data signal;
a gain control input configured to receive a gain control signal;
a gain controlled amplifier configured to receive the data signal and the gain control signal to create a gain adjusted signal, such that an amount gain adjustment is determined by the gain control signal;
one or more gain peaking control elements, connected to the gain controlled amplifier, configured to establish gain peaking in the gain adjusted signal; and
an output configured to provide the gain adjusted signal from the one or more gain peaking control elements to the distributed amplifier;
two or more amplifier cells, each amplifier cell comprising:
an amplifier cell input configured to receive the gain adjusted signal;
two or more amplifiers, connected in a cascode configuration, to amplify the gain adjusted signal to create an amplified signal; and
an amplifier cell output configured to carry the amplified signal;
an input path configured to receive an input signal and distribute the input signal to the two or more amplifier cells, the input path including one or more inductors that cancel input parasitic capacitance from the two or more amplifier cells; and
an output path connected to the amplifier cell output of the two or more amplifier cells to receive the amplified signal, the output path including one or more inductors that cancel output parasitic capacitance from the two or more amplifier cells.
2. The distributed amplifier of claim 1 wherein the one or more gain peaking control elements comprise inductors.
3. The distributed amplifier of claim 1 further comprising one or more emitter follower circuits having an emitter follower input connected to the input path and an emitter follower output connected to the amplifier cell input, the one or more emitter follower circuits configured to perform frequency specific gain adjustment in the amplified signal created by the one or more amplifier cells.
4. The distributed driver of claim 1 wherein an inductor from the input path and an inductor from the output path are associated with each amplifier cell.
5. The distributed driver of claim 1 further comprising a degeneration network connected to the gain controlled amplifier, the degeneration network configured to adjust low frequency gain.
6. The distributed driver of claim 1 wherein the variable gain amplifier further comprises one or more termination resistors configured to establish the gain of the gain controlled amplifier and set the output impedance of the variable gain amplifier.
7. The distributed driver of claim 1 wherein the two or more amplifier cells are configured in an open collector configuration.
8. The distributed driver of claim 3 wherein the emitter follower circuit further comprises a variable current source configured to control the frequency specific gain adjustment.
9. A distributed amplifier with variable gain control comprising:
a gain control circuit comprising a gain control circuit input, a gain control circuit output, one or more gain control amplifiers, and one or more gain peaking control elements located between a variable gain amplifier and an output, such that an amount gain adjustment is determined by a gain control signal which is received on a gain control signal input of the gain control circuit and the gain control circuit generating a gain adjusted signal; and
the distributed amplifier comprising:
an input path configured to receive an input signal including the gain adjusted signal and distribute the input signal to two or more amplifier cells, the input path including one or more inductors that cancel input parasitic capacitance from the two or more amplifier cells;
two or more amplifier cells configured with amplifiers in a cascode configuration to amplify a received signal to create an amplified signal;
an output path connected to the amplifier cell output of the two or more amplifier cells to receive the amplified signal, the output path including one or more inductors that cancel output parasitic capacitance from the two or more amplifier cells.
10. The distributed amplifier of claim 9 wherein gain peaking control elements comprise inductors.
11. The distributed amplifier of claim 9 further comprising a termination load connected between the gain peaking control elements and the gain control circuit output.
12. The distributed amplifier of claim 9 further comprising one or more emitter follower circuits, associated with each amplifier cell, that are located between the input path and the two or more amplifier cells, wherein the emitter follower circuits are configured to perform frequency specific gain adjustment in the amplified signal.
13. The distributed driver of claim 12 wherein the emitter follower circuit further comprises a variable current source configured to control the frequency specific gain adjustment.
14. The distributed amplifier of claim 9 wherein the gain control circuit further comprises a degeneration network connected to the gain control amplifier, the degeneration network configured to adjust low frequency gain.
15. The distributed driver of claim 1 wherein the two or more amplifier cells are configured in an open collector configuration.
16. A method for creating an amplified signal with frequency specific magnitude adjustment comprising:
receiving the input signal, an input signal to be transmitted on an optic fiber as an optic signal;
adjusting gain applied to the input signal with a variable gain amplifier, based on a control gain signal, to create a gain adjusted signal, such that adjusting of the gain includes introducing frequency specific magnitude adjustment to the input signal for gain peaking, gain shaping, or both;
receiving the gain adjusted signal on an amplifier input path, the amplifier input path having an inductance that cancels input parasitic capacitance of two or more amplifier cells;
amplifying the input signal after frequency specific magnitude adjustment with the two or more amplifier cells;
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 an inductance that cancels output parasitic capacitance of the two or more amplifier cells; and
presenting the combined output signal on an output.
17. The method of claim 16 wherein an inductor from the input path and an inductor from the output path are associated with each amplifier cell, and the inductors are realized as integrated transmission line elements.
18. The method of claim 16 wherein the two or more amplifier cells are configured in an open collector configuration.
19. The method of claim 16 further introducing frequency specific gain control with an emitter follower circuit that is associated with at least one of the two or more amplifier cells, the emitter follower circuit including a variable current source configured to control an amount of frequency specific gain control.
20. The method of claim 16 wherein the two or more amplifier cells further comprise a first input and a second input, the first and second inputs are configured to accept a differential signal, and the first input connects to a first emitter follower circuit and the second input connects to a second emitter follower circuit.