Transimpedance amplifier with linearized transconductance feedback
View Patent ↗The invention relates to a feedback circuit for a transimpedance amplifier, which is typically used for converting an input current from a photodiode into an output voltage. The feedback circuit of the present invention linearizes the transconductance feedback, as the input current signal varies, by providing a constant current source for supplementing the DC feedback current through a bypass transistor, thereby reducing a variation in the low frequency cut off.
1. A transimpedance amplifier comprising:
an amplifier circuit for converting a variable input current signal, which has AC and DC components, into an output voltage; and
a feedback circuit generating a feedback voltage signal with AC and DC components from the output voltage, the feedback circuit including:
a feedback amplifier/low pass filter, defining a low frequency cut off, for removing the AC component of the feedback voltage signal;
a bypass transistor, which receives the DC component of the feedback voltage signal and generates a DC feedback current substantially equal to the DC component of the input current signal for removing the DC component of the input current signal, the feedback circuit having a feedback gain; and
a linearizing circuit for linearizing the feedback gain as the input current signal varies, including a constant current source for supplementing the DC feedback current through the bypass transistor, thereby reducing a variation in the low frequency cut off caused by the variation in the input current;
wherein the input current signal ranges from a low to a high current; and
wherein the constant current source generates a constant current equal to or greater than the high current.
2. The transimpedance amplifier according to claim 1 , wherein the constant current source generates a constant current 2 to 3 times greater than the high current.
3. The transimpedance amplifier according to claim 1 , wherein the linearizing circuit further comprises a gain resistance for converting the DC component of the feedback voltage into the DC feedback current.
4. A transimpedance amplifier comprising:
an amplifier circuit for converting a variable input current signal, which has AC and DC components, into an output voltage; and
a feedback circuit generating a feedback voltage signal with AC and DC components from the output voltage, the feedback circuit including:
a feedback amplifier/low pass filter, defining a low frequency cut off, for removing the AC component of the feedback voltage signal;
a bypass transistor, which receives the DC component of the feedback voltage signal and generates a DC feedback current substantially equal to the DC component of the input current signal for removing the DC component of the input current signal, the feedback circuit having a feedback gain;
a linearizing circuit for linearizing the feedback gain as the input current signal varies, including a constant current source for supplementing the DC feedback current through the bypass transistor, thereby reducing a variation in the low frequency cut off caused by the variation in the input current; and
a current mirror for mirroring the DC component of the feedback current, which removes the DC component of the input current signal.
5. The transimpedance amplifier according to claim 4 , wherein the input current signal ranges from a low to a high current; and wherein the constant current source generates a constant current equal to or greater than the high current.
6. A transimpedance amplifier comprising:
an amplifier circuit for converting a variable input current signal, which has AC and DC components, into an output voltage; and
a feedback circuit generating a feedback voltage signal with AC and DC components from the output voltage, the feedback circuit including:
a feedback amplifier/low pass filter, defining a low frequency cut off, for removing the AC component of the feedback voltage signal;
a bypass transistor, which receives the DC component of the feedback voltage signal and generates a DC feedback current substantially equal to the DC component of the input current signal for removing the DC component of the input current signal, the feedback circuit having a feedback gain; and
a linearizing circuit for linearizing the feedback gain as the input current signal varies, including a constant current source for supplementing the DC feedback current through the bypass transistor, thereby reducing a variation in the low frequency cut off caused by the variation in the input current;
wherein the constant current source includes a current source transistor and a current mirror pair.
7. The transimpedance amplifier according to claim 6 , wherein the input current signal ranges from a low to a high current; and wherein the constant current source generates a constant current equal to or greater than the high current.
8. The transimpedance amplifier according to claim 7 , wherein the constant current source generates a constant current 2 to 3 times greater than the high current.
9. The transimpedance amplifier according to claim 6 , wherein the linearizing circuit further comprises a gain resistance for converting the DC component of the feedback voltage into the DC feedback current.
10. The transimpedance amplifier according to claim 6 , further comprising a current mirror for mirroring the DC component of the feedback current, which removes the DC component of the input current signal.
11. The transimpedance amplifier according to claim 5 , wherein the constant current source generates a constant current 2 to 3 times greater than the high current.
12. The transimpedance amplifier according to claim 4 , wherein the linearizing circuit further comprises a gain resistance for converting the DC component of the feedback voltage into the DC feedback current.
13. The transimpedance amplifier according to claim 4 , wherein the constant current source includes a current source transistor and a current mirror pair.
14. The transimpedance amplifier according to claim 1 , further comprising a current mirror for mirroring the DC component of the feedback current, which removes the DC component of the input current signal.
15. The transimpedance amplifier according to claim 1 , wherein the constant current source includes a current source transistor and a current mirror pair.