Computational circuits

Chapter 9.7 Computational circuits

Lessons In Electric Circuits Volume III – Semiconductors Book
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Lessons In Electric Circuits Volume III – Semiconductors Book

  • 9.7. COMPUTATIONAL CIRCUITS4351.25 VVcontrol = 0 to 5 V33033033015015047 nF47 nF47 nF47 nF47 nFFigure 9.20:PIN diode attenuator: PIN diodes function as voltage variable resistors. After Lin 467,[1].The PIN diodes are arranged in a π-attenuator network. The anti-series diodes cancel someharmonic distortion compared with a single series diode. The fixed 1.25 V supply forwardbiases the parallel diodes, which not only conducting DC current from ground via the resistors,but also, conduct RF to ground through the diodes’ capacitors. The control voltage Vcontrol,increases current through the parallel diodes as it increases. This decreases the resistanceand attenuation, passing more RF from input to output. Attenuation is about 3 dB at Vcontrol=5 V. Attenuation is 40 dB at Vcontrol= 1 V with flat frequency response to 2 gHz. At Vcontrol=0.5 V, attenuation is 80 dB at 10 MHz. However, the frequency response varies too much touse. 467,[1]9.7Computational circuitsWhen someone mentions the word ”computer,” a digital device is what usually comes to mind.Digital circuits represent numerical quantities in binaryformat: patterns of 1’s and 0’s repre-sented by a multitude of transistor circuits operating in saturated or cutoff states. However,analog circuitry may also be used to represent numerical quantities and perform mathematicalcalculations, by using variable voltage signals instead of discrete on/off states.Here is a simple example of binary (digital) representation versus analog representation ofthe number ”twenty-five:”