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Digitally Controlled NMR RF PIN Diode Attenuator

IP.com Disclosure Number: IPCOM000039088D
Original Publication Date: 1987-Apr-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Argyrakis, SN: AUTHOR [+2]

Abstract

A digitally controlled PIN diode attenuator is disclosed which provides for accurate computer control of nuclear magnetic resonance (NMR) RF power. As shown in the figure, control voltage signal +Vin (provided by a computer) is transmitted to an inverting unity gain amplifier which produces an inverted output voltage signal -Vo, and to a non-inverting unity gain amplifier which produces a non-inverted output voltage signal +Vo. That is, signal +Vo has the same polarity as input control signal +Vin. Inverted signal -Vo is provided across current limiting resistor R1, and non-inverted signal +Vo is provided across current- limiting resistor R2. Inductor L1 follows resistor R1 to block RF current while offering virtually no opposition to direct current I1.

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Digitally Controlled NMR RF PIN Diode Attenuator

A digitally controlled PIN diode attenuator is disclosed which provides for accurate computer control of nuclear magnetic resonance (NMR) RF power. As shown in the figure, control voltage signal +Vin (provided by a computer) is transmitted to an inverting unity gain amplifier which produces an inverted output voltage signal -Vo, and to a non-inverting unity gain amplifier which produces a non-inverted output voltage signal +Vo. That is, signal +Vo has the same polarity as input control signal +Vin. Inverted signal -Vo is provided across current limiting resistor R1, and non-inverted signal +Vo is provided across current- limiting resistor R2. Inductor L1 follows resistor R1 to block RF current while offering virtually no opposition to direct current I1. Inductor L2 follows resistor R2 to block RF current while offering virtually no opposition to direct current I2. Diode D1 (as well as diode D2) is a PIN diode which is essentially a controllable variable resistance. (A PIN diode is generally used as an on/off device in switching and phase-shifting circuits, or as a variable resistance, controlled by the forward bias current, in attenuators and modulators.) Current I1 provides direct current bias of diode D1 and current I2 provides direct current bias of diode D2. When diode D2 is forward biased (ON), the resistance of diode D2 provides for an RF current to flow through diode D2 from RF INPUT to RF OUTPUT. Diode D2 i...