Transimpedance amplifier with variable inductance input reducing peak variation over gain
A transimpedance amplifier (TIA) structure includes an input node with a variable inductance component serving to reduce variation in peak amplitude over different gain conditions. According to certain embodiments, an inductor at the TIA input has a first node in communication with a Field Effect Transistor (FET) drain, and a second node in communication with the FET source. A control voltage applied to the FET gate effectively controls the input inductance by adding a variable impedance across the inductor. Under low gain conditions, lowering of inductance afforded by the control voltage applied to the FET reduces voltage peaking. TIAs in accordance with embodiments may be particularly suited to operate over a wide dynamic range to amplify incoming electrical signals received from a photodiode.
1. A method comprising:
adding variable impedance at an input terminal of a variable-gain transimpedance amplifier that is coupled to a photodetector in order to reduce a peak voltage at an output terminal of the transimpedance amplifier, by:
determining a control voltage according to a gain of the transimpedance amplifier, and
adding the variable impedance by applying the control voltage to a variable inductance component located between the photodetector and the input terminal,
wherein the variable inductance component consists of a two-terminal inductor and a switch, the switch comprising,
a control contact receiving the control voltage,
a first contact in communication with a first node of the two-terminal inductor, the first node in communication with a photodiode, and
a second contact at a second node of the two-terminal inductor, the second node in communication with the input terminal.
2. The method of claim 1 wherein the switch comprises a transistor.
3. The method of claim 2 wherein the switch comprises a field-effect transistor (Fet).
4. The method of claim 3 wherein:
the control contact comprises a gate of the Fet in communication with a variable voltage source;
the first contact comprises a drain of the Fet; and
the second contact comprises a source of the Fet.
5. The method of claim 3 wherein the Fet comprises a JFET.
6. The method of claim 3 wherein the Fet comprises a FinFet.
7. The method of claim 3 wherein the Fet comprises a MOSFET.
8. The method of claim 7 wherein the Fet comprises a SiGe bi-CMOS field effect transistor having:
a gate receiving the control voltage from a variable voltage source through a resistor,
a drain at a first node of the inductor and in communication with a photodiode, and
a source at a second node of the inductor and in communication with the input terminal.
9. The method of claim 8 wherein the transimpedance amplifier is configured to operate with a dynamic range of about 18 dB to about 20 dB.
10. The method of claim 8 wherein the transimpedance amplifier is configured to operate with a dynamic range of about 15 dB to about 18 dB.
11. The method of claim 8 wherein the variable control voltage is configured to reduce the peak voltage at the output terminal under low gain conditions.
12. The method of claim 1 further comprising providing another two-terminal inductor between the photodiode and the input terminal.
13. The method of claim 1 wherein the input terminal is in electrical communication with the photodiode across a chip boundary.
14. The method of claim 1 wherein the transimpedance amplifier is configured to operate with a dynamic range of about 18 dB to about 20 dB.
15. The method of claim 1 wherein the transimpedance amplifier is configured to operate with a dynamic range of about 15 dB to about 18 dB.
16. The method of claim 1 wherein the variable control voltage is configured to reduce the peak voltage at the output terminal under low gain conditions.
17. The method of claim 1 wherein the peak voltage is reduced by about 3 dB.
18. The method of claim 13 wherein further comprising providing another two-terminal inductor between the photodiode and the chip boundary.
19. The method of claim 1 , wherein the gain of the transimpedance amplifier is controlled using a gain voltage, and wherein the control voltage is determined using the gain voltage.
20. The method of claim 1 , wherein the variable impedance decreases in response to the gain of the transimpedance amplifier decreasing, and
wherein the variable impedance increases in response to the gain of the transimpedance amplifier increasing.