TRANSIMPEDANCE PRE-AMPLIFIER

• Main Author: EDDINS, WILLIAM T
• Format: Patent
• Language: English; French
• Published: 30.10.1984
• Edition: 3
• Subjects: AMPLIFIERS; BASIC ELECTRONIC CIRCUITRY; ELECTRICITY

A transimpedance pre-amplifier is used in connection with optical detectors and is designed to obtain low noise, low distortion and flat frequency response simultaneously. The amplifier design accomplishes low distortion and flat frequency response over a wide range of input signals by designing the pre-amplifier circuitry in such a manner as to compensate for the phase shift introduced by a feedback network connected across the input and output of the amplifier. This adjustment allows the feedback network to be of such a value as to effectively control any thermal noise introduced by the feedback resistor-input capacitance system. This compensation for the phase shift allows the phase margin and therefore stability to be controlled by means of the load impedance on the output transistor of the amplifier circuit. The result of such new relationship is that the amplifier may be designed based upon the desired location of the pole by adjusting the feedback resistance in such a manner as to negate the effects of the thermal feedback and from such calculation the load impedance connected across the output of the transistors which comprise the amplifier section are then determined by the equations derived.