METHOD AND APPARATUS FOR CONVERSIONLESS DIRECT DETECTION
A conversionless direct detection system for detecting signals having a very large dynamic range, with a virtually unlimited bandwidth utilizes a successive detection approach having successive log amplifier gain stages, with each gain stage involving simultaneous use of an RF transistor to perform both limiting and logging functions. FET transistors are used to extend the operating range beyond 200 GHz, with the self-bias in combination with a drain resistor limiting voltage and current swings. A log video output is tapped off the source resistor and is coupled to a buffering stage, with the outputs of the buffering stage summed to accommodate very large dynamic range swings of the input voltage, with successive stages saturating at different points to operate at different and contiguous regions, thus to provide the wide dynamic range. The limited RF signal is tapped off the drain resistor, with the stages connected in series to provide the limited RF output as the output of the last stage.