Amplifiers – With semiconductor amplifying device – Including atomic particle or radiant energy impinging on a...
Reexamination Certificate
2002-04-25
2003-07-08
Choe, Henry (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including atomic particle or radiant energy impinging on a...
C330S110000, C330S305000, C250S2140AG
Reexamination Certificate
active
06590455
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and/or architecture for implementing amplifiers generally and, more particularly, to a method and/or architecture for implementing a common-base amplifier with a high input overload capability and/or tunable transimpedance.
BACKGROUND OF THE INVENTION
One conventional approach for tuning the transimpedance response of an amplifier is to change the bias current of a common-base input stage. Varying the bias current varies the complex input impedance and voltage gain which changes the overall transimpedance response. However, dramatic changes in the bias current can profoundly change the overload capability of the transimpedance amplifier (TIA). In general, a peaked response is often due to wire-bond parasitics which can result in intersymbol interference (ISI). Such parasitics can be suppressed by reducing the bias current and effective input inductance of a common-base input stage. However, reducing the bias current can severely degrade overload performance. In order to satisfy the need for high current overload capability, a number of approaches for implementing common-base transimpedance pre-amplifier topologies are commonly used.
One such conventional approach is the implementation of common-base input stages that are capable of high input currents (e.g., Vanisri, Tongtod, Toumazou, Chris, “Integrated High Frequency Low-Noise Current-Mode Optical Transimpedance Preamplifiers: Theory and Practice”, IEEE JSSSC, vol. 30, no. 6, June, 1995, pp. 677-685). However, such circuits are biased with a collector current that equals or exceeds the overload current condition. Such an approach typically results in significant shot noise degradation and potential transimpedance gain-bandwidth degradation.
Another conventional common-base approach for improving overload current performance is to use a common-base differential switch to switch between a successive amplifier and the direct output based on the detected received power level (e.g., Van den Broeke, L. A. D., and Nieuwkerk, A. J., “Wide-Band Integrated Optical Receiver with Improved Dynamic Range Using a Current Switch at the Input”, IEEE JSSSC, vol. 28, no. 7, July 1993, pp. 862-864).
Referring to
FIG. 1
, a circuit
10
is shown implementing a conventional common-base input stage. The common-base input allows high input overload capability. However, increasing the current Ic
1
such that the current Ic
1
>an Overload current (Ioverload) specification (typically>2 mA) can result in higher input referred shot noise (i.e.,
2
qIc
1
). In addition, higher current Ic
1
can result in a peaked transimpedance response which can introduce undesirable noise, large signal transient distortion, and potential instability. However, the current Ic
1
must be set>Ioverload (2 mA) in order to maintain low TIA distortion.
Referring to
FIG. 2
, a circuit
20
is shown implementing another conventional common-base input stage. A common-base differential input is used to switch the input to either (i) a direct output when a high input current is detected, or (ii) a successive TIA amplifier when a low input current is detected. However, as in other conventional common-base stages, a high DC collector current Ic
1
, greater than the maximum signal current (2 mA), is maintained in order to avoid signal clipping at the input. As in the circuit
10
, additional noise and transimpedance-bandwidth peaking distortion can result.
Referring to
FIG. 3
, a DC overload performance of a conventional common-base TIA design is shown. A CB collector bias current of 1.5 mA only provides about 1.4 mA of overload current capability before the output voltage clips. In order to obtain high overload current from a common-base TIA, the quiescent collector current of the common-base transistor must be greater than the maximum input current seen by the TIA of the circuit
20
of Van den Broeke.
FIG. 3
shows the DC output voltage versus peak input current Ipd-peak for various common-base collector biases Ic
1
. High overload is obtained at higher collector biases. However, higher collector current bias also increases noise, gain peaking, large signal overshoot distortion, and potential circuit instability.
Referring to
FIG. 4
, an Overload Performance with an input current Iin=1.5 mA p-p for a conventional CB design (Ic
1
=1.5 mA) is shown. The waveform
40
illustrates the input current Iin (Ipd-peak). The waveform
42
illustrates the onset of duty cycle distortion at the output of the pre-amplifier stage. The waveform
44
illustrates the onset of duty cycle distortion at the output.
Referring to
FIG. 5
, an Overload Performance with an input current Iin=2 mA p-p for a conventional CB design (Ic
1
=1.5 mA) is shown. The waveform
40
′ illustrates the input current Iin (Ipd-peak). The waveform
42
′ illustrates significant duty cycle distortion at the output of the pre-amplifier stage. The waveform
44
′ illustrates significant duty cycle distortion at the output.
Referring to
FIG. 6
, an Overload Performance with an input current Iin=2.5 mA p-p for a conventional CB design (Ic
1
=1.5 mA) is shown. The waveform
40
″ illustrates the input current Iin (Ipd-peak). The waveform
42
″ illustrates severe duty cycle distortion at the output of the pre-amplifier stage. The waveform
44
″ illustrates severe duty cycle distortion at the output.
It would be desirable to implement a transimpedance amplifier that enables the transimpedance response to be tuned without substantially compromising overload performance.
SUMMARY OF THE INVENTION
The present invention concerns an apparatus comprising a common-base amplifier circuit and a control circuit. The amplifier circuit may be configured to generate an output signal having a transimpedance bandwidth in response to an input signal. The control circuit may be (i) coupled between the output signal and the input signal and (ii) configured to implement input signal control to provide input overload current capability.
The objects, features and advantages of the present invention include implementing a common-base amplifier with high input overload and tunable transimpedance that may (i) implement high dynamic range transimpedance amplifiers (TIAs) that may be suitable for next generation 10 Gb/s and 40 Gb/s optical receiver applications, (ii) provide state of the art transimpedance amplification for avalanche photodiodes (APDs) and heterojunction photo-transistors (HPTs) with responsivities in a range of 1-10 A/W p-p, (iii) have an overload specification that may be more aggressive than those imposed by typical 10 Gb/s positive-intrinsic-negative (PIN) diode technologies, and/or (iv) provide a TIA which may handle high overload currents (e.g., as defined by a particular design specification) while maintaining low duty cycle and overshoot distortion (e.g., as defined by a particular design specification).
REFERENCES:
patent: 5216386 (1993-06-01), Wyatt
patent: 6069534 (2000-05-01), Kobayashi
patent: 6404281 (2002-06-01), Kobayashi
“Wide-Band Integrated Optical Receiver with Improved Dynamic Range Using a Current Switch at the Input”, By L.A.D. van den Broeke and A.J. Nieuwkerk, IEEE Journal of Solid-State Circuits, vol. 28, No. 7, Jul. 1993, pp. 862-864.
“Integrated High Frequency Low-Noise Current-Mode Optical Transimpedance Preamplifiers: Theory and Practice”, By Tongtod Vanisri and Chris Toumazou, IEEE Journal of Solid-State Circuits, vol. 30, No. 6, Jun. 1995, pp. 677-685.
Kobayashi, Kevin W., “Method and/or Apparatus for Controlling a Common-Base Amplifier”, U.S. Ser. No. 10/123,503, Filed Apr. 16, 2002.
Choe Henry
Christopher P. Maiorana P.C.
Sirenza Microdevices, Inc.
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