Dynamic Range Extension of Schottky Detectors - App Note

Detectors are essentially low sensitivity receivers which function on the basis of direct rectification of the RF signal through the use of a non-linear resistive element - a diode. Generally detectors can be classified into two distinct types: the small-signal type, also known as square-law detectors; and the large-signal type, also known as linear or peak detectors. The small-signal detector operation is dependent on the slope and curvature of the VI characteristic of the diode in the neighborhood of the bias point. The output of the detector is proportional to the power input to the diode, that is, the output voltage (or current) is proportional to the square of the input voltage (or current), hence the term "square law" (see Figure 1). The large-signal detector operation is dependent on the slope of the VI characteristic in the linear portion, consequently the diode functions essentially as a switch. In large-signal detection, the diode conducts over a portion of the input cycle and the output current of the diode follows the peaks of the input signal waveform with a linear relationship between the output current and the input voltage. The square law dynamic range may be defined as the difference between the power input for 1 dB deviation from the ideal square law response (compression point) and the power input corresponding to the tangential signal sensitivity (TSS).