Technology Commercialization and Partnerships | BSA 96-23: Monolithic Amplifier with Stable, Hirgh Resistance Feedback

Category: electronics & instrumentation

BSA 96-23: Monolithic Amplifier with Stable, Hirgh Resistance Feedback

BNL Reference Number: BSA 96-23

Patent Status: U.S. Patent Number 5,793,254 was issued on August 11, 1998

Summary

This invention comprises a monolithic amplifier that includes a stable high resistance feedback circuit and a dynamic bias circuit. The dynamic bias circuit is formed with active elements matched to those in the amplifier and feedback circuit to compensate for variations in the operating and threshold voltages thereby maintaining a stable resistance in the feedback circuit.

Description

This monolithic charge sensitive amplifier achieves a stable, high resistance feedback using commercially available CMOS fabrication methods. The feedback resistance of this amplifier exhibits a low sensitivity to variations in both manufacturing process parameters such as threshold voltage and operating parameters such as supply voltage and temperature. This feedback exhibits a desirably low parasitic feedback capacitance, and this feedback resistance will be maintained without the need for any adjustments. This monolithic charge sensitive amplifier, having a stable, high resistance feedback circuit, will remain continuously sensitive to input signals even in the presence of a leakage current from the input signal source. This continuous sensitivity is maintained by a compensating reduction in the feedback resistance in the presence of a leakage current from the input source which prevents the amplifier from entering saturation. The pole-zero circuit formed in accordance with the present invention compensates both the linear and non-linear characteristics of the feedback circuit.

Benefits

Charge sensitive amplifiers usually require a high value feedback resistor to achieve low noise performance. However, high value resistors are difficult to implement using conventional CMOS fabrication methods. Several circuit configurations have been used in the prior art to use an active element to achieve the desired high resistance in a monolithically formed charge sensitive amplifier. These circuit configurations suffer from several disadvantages such as periods of inoperability, feedback instability, and/or very large variations in the resistance of the feedback element due to variations in process, temperature, and power supply voltage. This invention comprises a monolithic charge sensitive amplifier which has a stable, high resistance feed-back circuit which will remain continuously sensitive to input signals even in the presence of a leakage current from the input signal source.

Applications and Industries

Semiconductor radiation detectors are now used in a large variety of fields, including nuclear physics, X-ray and gamma ray astronomy, and nuclear medicine. Their imaging capabilities, good energy resolution, and the ability to fabricate compact systems are very attractive features, in comparison with other types of detectors, such as gas detectors and scintillators. Medical, imaging, nuclear nonproliferation, non-destructive detection, radiation imaging, and homeland security applications.