Detector circuit with dual-diode compensation

A detector circuit comprising:

• a first diode and a second diode formed as a monolithic structure upon a common substrate;
• a capacitor connected in parallel to said second diode, said second diode detecting an input signal applied to a terminal thereof;
• means for heating said substrate;
• means connected to said first diode for energizing said heating means, said first diode serving as a sensor of temperature of said substrate to activate said energizing means to energize said heating means for maintaining said substrate at a predetermined temperature;
• means for biasing said first diode and said second diode to maintain equal values of bias voltage in said first and said second diodes;
• and
• differential amplifier means connected to each of said diodes for amplifying signals appearing across each of said diodes, a signal appearing across said first diode comprising a voltage produced by said bias current in said first diode, a signal appearing across said second diode comprising a bias voltage produced by a bias current flowing in said second diode plus the voltage of a detected input signal, said differential amplifier means amplifying said detected signal voltage while rejecting bias voltages produced by said bias currents as a common mode signal by virtue of differential operation of said amplifying means.

A detector circuit comprising:

• a first diode and a second diode formed monolithically on a common substrate, each of said diodes having a first terminal and a second terminal, the second terminal of each of said diodes being connected together as a common terminal;
• a capacitor, said second diode being connected together via said common terminal to said capacitor for detection of an input signal applied to the first terminal of said second diode;
• means for heating said substrate;
• means including a third diode for energizing said heating means, said third diode being thermally coupled to said substrate for sensing the temperature thereof to activate said energizing means to energize said heating means for maintaining said substrate for stabilizing a temperature thereof;
• amplifying means having a first channel connected to the first terminal of said first diode and a second channel connected to the common terminal of said first and said second diodes;
• biasing means connected between the first terminal of said first diode and said common terminal and further connected between said first terminal of said second diode and said common terminal for impressing equal bias currents in said first and said second diodes;
• and wherein
• said second channel of said amplifying means includes a differential amplifier having one input terminal receiving the bias voltage resulting from the sum of the two bias currents from the common terminal, and a second input terminal connected to a reference voltage to subtract the sum of the bias currents from an output signal of said amplifying means;
• and
• the detection of the input signal at said second diode induces a detected signal voltage at said first diode, said first channel of said amplifying means including a feedback amplifier of higher gain than said differential amplifier of said second channel for amplifying detected signals induced in said first diode, said bias means cooperating with said feedback amplifier to limit signals of said first diode to a relatively small value, said differential amplifier of said second channel amplifying signals of both small and large values;
• and wherein
• said amplifying means includes means for summing together an output signal of said feedback amplifier of said first channel and an output signal of said differential amplifier of said second channel, said feedback amplifier of said first channel being constructed of low-drift circuitry to ensure that a signal outputted by said summing means of said amplifying means is essentially free of thermally induced drift at said first and said second diodes.