GB1501730A - Radio-frequency detector - Google Patents

Abstract

1501730 Diode detectors INTERNATIONAL STANDARD ELECTRIC CORP 30 April 1975 [7 May 1974] 18046/75 Headings H3Q and H3T In a r.f. detector operating linearly down to very low signal levels having two branches, each including a diode D1, D2, Fig. 3, which conducts during a half-cycle of different polarity from the other and a resistor R1, R2 in series with each diode to supplement the forward resistance of each diode to provide a required input impedance, each diode is biased to its knee voltage by a respective bias voltage U V1 , U V2 provided by means Al, A2 simulating such voltages whereby symmetrical half-wave currents are derived in the initial regions of the diodes i.e. at very low input signal level and a demodulated signal is obtained at Vo, from the arithmetic mean of the diode currents derived from an input signal Vi, by evaluating means A1, A2 which do not reflect impedance changes into the input impedance of the detector. As shown a bias source U is connected to an integrated or discrete component inverting operational amplifier A2 which provides a virtual bias source U v2 with reverse sign and a source resistance tending to zero but with equal amplitude. Similarly an operational amplifier Al having a negative feedback network GK provides a virtual bias source U v1 with equal sign and a source impedance tending to zero. The bias source U can be replaced by a resistor R3 and a diode D3, Fig. 5, and non-linearity for low input voltages Vi > 50 mV can be compensated for (Fig. 6, not shown) by including a diode D4 in series with a resistor R4 in the negative feedback network of A1. The output can be from A1 and ground (Fig. 4, not shown) or as shown from R7 and R8 which function to eliminate the D.C. component of the output signal. In the arrangements described above only one branch and only one half cycle is used to derive the demodulated signal, while the second branch only serves to ensure a defined input resistance equal during both half-cycles. In a fullwave circuit (Fig. 7, not shown) amplifier A2 is replaced with circuitry similar to amplifier Al and a demodulated output signal is derived from a differential amplifier DA. Schottky diodes may be used instead of point-contact diodes for frequencies above the v.h.f. region. Resistors R1 and R2 may be in chip form.