Claims
- 1. A pseudo-differential transimpedance amplifier comprising:
a first input amplifier configured to receive an AC-coupled input signal and to generate a first pseudo-differential voltage; a second input amplifier configured to receive a DC-coupled input signal and to generate a second pseudo-differential voltage; and a DC compensation circuit coupled between an output of the first input amplifier and an input of the second input amplifier, wherein the DC compensation circuit cancels a portion of the DC-coupled input signal to adjust a DC offset of the second pseudo-differential voltage.
- 2. The pseudo-differential transimpedance amplifier of claim 1, wherein the DC compensation circuit comprises:
a peak-hold circuit coupled to the output of the first input amplifier and configured to track the amplitude of the first pseudo-differential voltage; and a voltage-to-current converter coupled to an output of the peak-hold circuit and configured to generate a correction current for the second input amplifier.
- 3. The pseudo-differential transimpedance amplifier of claim 1, further comprising a differential output stage coupled to the output of the first input amplifier and the output of the second input amplifier, wherein the differential output stage generates a pair of differential output voltages for the pseudo-differential transimpedance amplifier.
- 4. The pseudo-differential transimpedance amplifier of claim 1, wherein the AC-coupled input signal and the DC-coupled input signal correspond to input current signals of opposite polarities.
- 5. A receiver circuit comprising:
an optical detector configured to convert a light signal into an electrical current signal, wherein the optical detector has an AC-coupled output to provide a first representation of the electrical current signal with a first polarity and a DC-coupled output to provide a representation version of the electrical current signal with a second polarity; and a pseudo-differential amplifier configured to convert the electrical current signal into a pair of differential voltage signals, wherein the pseudo-differential amplifier has a first input amplifier coupled to the AC-coupled output of the optical detector to receive the first representation of the electrical current signal and a second input amplifier coupled to the DC-coupled output of the optical detector to receive the second representation of the electrical current signal.
- 6. The receiver circuit of claim 5, wherein the optical detector has a photodiode to generate the electrical current signal in response to the light signal, the first input amplifier is coupled to a cathode of the photodiode via a capacitor, and the second input amplifier is coupled to an anode of the photodiode.
- 7. The receiver circuit of claim 5, further comprising a DC correction circuit configured to minimize a DC component of the electrical current signal at an input of the second input amplifier, wherein the DC correction circuit is coupled between an output of the first input amplifier and the input of the second input amplifier
- 8. The receiver circuit of claim 7, wherein the DC correction circuit detects peak voltage levels at the output of the first input amplifier and generates corresponding correction currents to remove the DC component of the electrical current signal at the input of the second input amplifier.
- 9. A method for converting a unipolar current signal to a pair of differential voltage signals, the method comprising:
providing a first polarity of the unipolar current signal to a first input amplifier via a capacitor; providing a second polarity of the unipolar current signal to a second input amplifier; generating a compensation current responsive to the amplitude of the unipolar current signal; and adding the compensation current to an input of the second input amplifier to adjust a difference in DC levels between the output of the first input amplifier and an output of the second input amplifier.
- 10. The method of claim 9, wherein the compensation current reduces a substantial DC portion of the unipolar current signal at the input of the second input amplifier.
- 11. The method of claim 9, wherein the unipolar current signal is generated by a photodiode in response to a light signal.
- 12. The method of claim 9, further comprising tracking the amplitude of an output of the first input amplifier to provide an indication of the amplitude of the unipolar current signal;
- 13. The method of claim 12, wherein a peak-hold circuit tracks the amplitude of the output of the first input amplifier.
- 14. The method of claim 13, wherein a voltage controlled current source is coupled to an output of the peak-hold circuit to generate the compensation current.
- 15. An amplifier for converting an input current signal to a pair of differential output voltage signals, the amplifier comprising:
means for converting a first polarity of the input current signal to a first output voltage; means for converting a second polarity of the input current signal to a second output voltage; means for detecting peak levels of the first output voltage; means for generating a compensation current in response to the peak levels of the first output voltage; and means responsive to the compensation current for adjusting a DC offset of the second output voltage.
- 16. The amplifier of claim 15, wherein the input current signal is generated by a photodiode in response to a light signal, the first polarity of the input current signal is provided by a cathode of the photodiode, and the second polarity of the input current signal is provided by an anode of the photodiode.
- 17. The amplifier of claim 15, wherein the peak levels of the first output voltage indicate the amplitude of the input current signal.
- 18. The amplifier of claim 15, wherein the compensation current is responsive to a DC component of the input current signal.
- 19. The amplifier of claim 15, wherein the compensation current minimizes a difference in DC levels between the first output voltage and the second output voltage.
- 20. An optical receiver for translating a light signal into a pair of differential voltage signals, the optical receiver comprising:
means for converting the light signal to a unipolar current signal; means for AC-coupling a first polarity of the unipolar current signal to a first input amplifier; means for DC-coupling a second polarity of the unipolar current to a second input amplifier; and means for canceling a portion of the unipolar current at an input of the second input amplifier based on an output of the first input amplifier.
RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional Application No. 60/371,288, filed on Apr. 9, 2002, and entitled Pseudo-Differential Transimpedance Amplifier With Fast DC Offset Cancellation.
Provisional Applications (1)
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Number |
Date |
Country |
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60371288 |
Apr 2002 |
US |