Variable bandwidth transimpedance amplifier with one-wire interface

1. An adjustable bandwidth transimpedance amplifier comprising:

an amplifier configured to receive a current signal;

a feedback path coupling an input and an output of the amplifier; and

a selectable resistance in the feedback path, resistance of the selectable resistance controlled by a control signal, the selectable resistance comprises a plurality of resistances, the plurality of resistances switchably coupled to the feedback path, the plurality of resistances comprising a plurality of resistors, the plurality of resistors coupled in series and at least some of the resistors each having a switch coupled in parallel, the control signal determining whether the switches are open or closed, the control signal being coupled to a plurality of comparators, and an output of each comparator is coupled to a corresponding switch;

wherein the control signal is a voltage signal;

wherein a current on a signal path is an indication of the current signal provided to the adjustable bandwidth transimpedance amplifier; and

wherein the current on the signal path is provided by a current mirror.

2. The adjustable bandwidth transimpedance amplifier of claim 1 wherein the current mirror is coupled to an output of the amplifier having an input receiving the current signal.

3. The adjustable bandwidth transimpedance amplifier of claim 2 wherein the current mirror is formed by two gate coupled FETs.

4. The adjustable bandwidth transimpedance amplifier of claim 3 wherein the current mirror is coupled to a voltage-to-current converter.

5. A receiver optical subassembly including an adjustable bandwidth transimpedance amplifier, comprising:

a photodiode configured to receive an optical data signal;

an adjustable bandwidth transimpedance amplifier with an input coupled to an output of photodiode;

the adjustable bandwidth transimpedance amplifier comprising an amplifier receiving a current signal with a feedback path coupling an input and an output of the amplifier;

a selectable resistance in the feedback path, resistance of the selectable resistance controlled by a control signal, the selectable resistance comprises a plurality of resistances, the plurality of resistances are switchably coupled to feedback path, the plurality of resistances comprise a plurality of resistors, the plurality of resistors coupled in series and at least some of the resistors each have a switch coupled in parallel, the control signal determines whether the switches are open or closed, the control signal is coupled to a plurality of comparators, and an output of each comparator is coupled to a switch;

a signal path coupled to the adjustable bandwidth transimpedance amplifier, the signal path providing a pathway for a control signal for adjusting bandwidth of the adjustable bandwidth transimpedance amplifier wherein at least a portion of the signal path is coupled to an output of the photodiode, the portion of the signal path providing a pathway for a current indication signal indicating current generated by the photodiode wherein the current indication signal is provided by a current mirror, and

a further amplifier with an input coupled to an output of the adjustable bandwidth transimpedance amplifier and a dual output providing an output differential signal.

6. A method of operating a receiver optical subassembly, comprising:

generating a current signal in response to a data bearing incoming light signal by a photodiode;

providing the current signal to a transimpedance amplifier;

forming a signal indicative of the current signal by a current mirror;

placing the signal indicative of the current signal on a monitor/select pin;

receiving a control signal on the monitor/select pin;

adjusting a resistance of a feedback path of the transimpedance amplifier by utilizing a plurality of comparators to configure a plurality of switches coupled in parallel with a plurality of resistors, based on the control signal.

7. A five pin package including a photodiode and transimpedance amplifier comprising:

a housing with a window

a die within the housing;

five pins coupled to the housing and electrically coupled to the die, a first pin of the five pins providing a ground pin and a second pin of the five pins providing a power pin;

a photodiode within the housing and approximate the window, the photodiode positioned to receive light passing though the window;

the die including an adjustable bandwidth transimpedance amplifier, with the photodiode electrically coupled to an input of the adjustable bandwidth transimpedance amplifier;

the die further including a further amplifier with an input electrically coupled to an output of the adjustable bandwidth transimpedance amplifier and with two outputs forming a differential output, the differential output being coupled to a third pin of the five pins and a fourth pin of the five and a fifth pin of the five pins operatively coupled to a signal path for a current signal indicative of current generated by the photodiode and a feedback path of the adjustable bandwidth transimpedance amplifier to provide adjustment of a resistance of the feedback path, the fifth pin operatively coupled to the feedback path by at least one comparator, the resistance of the feedback path is a selectable resistance, and the output of the at least one comparator is coupled to the selectable resistance; and

wherein the current signal indicative of current generated by the photodiode is provided by a current mirror.

8. The five pin package including a photodiode and a transimpedance amplifier of claim 7 wherein the fifth pin is also coupled to the current mirror, which is operatively coupled to an output of the photodiode.

9. The five pin package including a photodiode and a transimpedance amplifier of claim 8 wherein the signal for providing adjustment of the bandwidth of the adjustable bandwidth transimpedance amplifier is a voltage signal.

10. The five pin package including a photodiode and a transimpedance amplifier of claim 9 wherein the current mirror is formed by two gate coupled FETs.

11. The five pin package including a photodiode and a transimpedance amplifier of claim 10 wherein the current mirror is coupled to a voltage-to-current converter.