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Variable PIN Attenuator

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This is a very useful RF attenuator circuit which works from 300KHz to the 3GHz range based on the quad PIN diode array HSMP-3816 from Avego.  The lower PIN diodes are biased at 1mA which gives about a 40 to 70 ohm impedance.  R5 can be increased to increase the RF input and output impedances of the circuit. 

The upper diodes are biased by the control voltage which varies between 0 and 10V.  The signal is essentially blocked when the control voltage is 0V and passes when the control voltage is high.   The beauty of this circuit is that a small current can control a higher power RF waveform.  

To create a control voltage of 0 to 10V use a voltage servo circuit.

Schematic of Variable RF Attenuator based on a Quad PIN Diode

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