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A compendium of application circuits for Xicor's digitally-controlled (XDCP) potentiometers

Posted: 08 Jun 2001     Print Version  Bookmark and Share


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Application Note AN115 AN115-1 A Compendium of Application Circuits for Xicor's Digitally-Controlled (XDCP) Potentiometers Chuck Wojslaw (March 1998) Introduction This Note lists a number of application circuits for Xicor's digitally-controlled (XDCP) potentiometers. The applica- tion circuits, shown in basic form, illustrate the wide variety of possible functions that can be implemented using the variability of the potentiometer in conjunction with stan- dard active devices like operational amplifiers and com- parators. The types of circuits include control circuits, converters, filters, signal processing circuits, regulators, waveshapers, analog computing circuits, and signal sources. In the detail design of these circuits, proper sup- ply filtering and proper grounding techniques must be used. Xicor's potentiometers are controlled through the 2-wire, 3-wire, or SPI computer serial-interfaces or buses. For front panel, pushbutton type applications, Xicor's pushpots are recommended. General technical publications and other Xicor application notes discuss the various computer serial-interfaces to the electronic potentiometer. Electronic Digitally-controlled (XDCP) potentiometers provide three powerful application advantages; (1) the variability and reliability of a solid-state potentiometer, (2) the flexibility of computer-based digital controls, and (3) the retentivity of nonvolatile memory used for the storage of multiple potentiometer settings or data. In addition, the packages of the potentiometers are completely compatible with other electronic components and hence reduce manufacturing assembly costs. Expanded versions of many of the circuits listed in this paper are available in other Xicor application notes. The reader is invited to examine the Application Note Index for these cases. Applications Figure 1. Basic Configurations of Electronic Potentiometers VR VW VR I Three terminal Potentiometer; Variable voltage divider Two terminal Variable Resistor; Variable current Xicor Application Note AN115-2 AN115 Application Circuits Noninverting Amplifier Voltage Regulator Offset Voltage Adjustment Comparator with Hysterisis + - VS VO R2 R1 VO = (1+R2/R1)VS R1 R2 Iadj VO (REG) = 1.25V (1+R2/R1)+Iadj R2 VO (REG)VIN 317 + - VS VO R2R1 VUL = {R1/(R1+R2)} VO(max) VLL = {R1/(R1+R2)} VO(min) 100K 10K10K 10K -12V+12V TL072 + -VS VO R2R1 } } LM308A Cascading TechniquesBuffered Reference Voltage - + +5V R1 +V -5V VW VREF VOUT OP-07 VW VW +V +V +V X (a) (b) +5V 2.2K LT311A VOUT = VW Xicor Application Note AN115 AN115-3 Application Circuits Attenuator Filter Inverting Amplifier Equivalent L-R Circuit + - VS VO R3 R1 VO = G VS -1/2 G +1/2 GO = 1 + R2/R1 fc = 1/(2RC) + - VS VO R2R1 ZIN = R2 + s R2 (R1 + R3) C1 = R2 + s Leq (R1 + R3) >> R2 + - VS Function Generator R2 R4 R1 = R3 = R4 + - VS R2 R1 R C } } VO = G VS G = - R2/R1 R2C1 R1 R3 ZIN + - R2 + - R1 } } RA RB frequency R1, R2, C amplitude RA, RB C LT1097 R2 = 2R1 VO Xicor Application Note AN115-4 AN115 Application Circuits I to V Converter Current Source Phase Shifter Capacitance Multiplier + - VO R3 R1 VO / IS = -R3(1+R2/R1) + R2 IS = VR/R + -VS VO R1 CIN = C (1 + R2/R1) + - Absolute Value Amplifier with Gain + -VR R1 R R2 Cin + -R1 }R1 R2 IS + - R1 R1 RL R1 IS R1 R C VO/VS = 1800 - 2tan-1 RC R1 C + - + - + - }R2 + + VS VR VOUT RRR 2R VO VS A1 A2 Level Detector VO = |VS| R1 R VOUT = High for VS < - VR R1 R2 VOUT = Low for VS > - VR R1 R2 R1 + R2 = RPOT AN115-5 Xicor Application Note AN115 Application Circuits Level Detector Time Delay + - VOUT VT>VW, VOUT = High VS + -R R C + - VH VL VW + - VTRANSDUCER (VT) VREFERENCE (VR) VT

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