Extended range sample and hold circuit

Abstract

An extended range sample and hold circuit for use in systems such as floating point amplifiers is disclosed. An input differential amplifier receives a varying analog signal which is passed by a transistor sample switch during a predetermined sample period to an integrating differential amplifier having a sample capacitor across its output and inverting input. The charge on the sample capacitor follows the input analog signal. The output of the integrating differential amplifier is connected to a nonlinear circuit which in turn is connected to the noninverting input of an output differential amplifier. The nonlinear circuit provides a resistive path for small signals so that a fraction of the voltage across the sample capacitor is presented at the input to the output differential amplifier. As the signal becomes larger, a nonlinear portion of the circuit provides a signal at the input to the output differential amplifier that approaches the charge on the sample capacitor at one extreme. As the signal becomes smaller, it approaches the fractional portion at the other. The output amplifier provides a feedback loop to the input amplifier. Also, a transistor switch identical to the transistor sample switch is connected to a capacitor identical to the sample capacitor and connected to the noninverting input of the integrating differential amplifier to assure that transistor switch capacitance charge transfer is equal on the inverting and noninverting inputs of the integrating differential amplifier.