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Digitally Controlled Multipurpose Analog Circuit

IP.com Disclosure Number: IPCOM000091076D
Original Publication Date: 1969-Oct-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 33K

Publishing Venue

IBM

Related People

Esteban, DJ: AUTHOR

Abstract

This circuit performs, under digital control, various analog functions with linear transfer characteristics. A minimum number of elements is used.

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Digitally Controlled Multipurpose Analog Circuit

This circuit performs, under digital control, various analog functions with linear transfer characteristics. A minimum number of elements is used.

All of the functions are programmed by connections on circuit card pins. Several analog functions can be performed on a time-sharing basis. The basic circuit includes one analog input, gated logic inputs X1 and X2, G1 and G2 gate inputs, and an analog output. The analog input bin is connected to operational amplifier A1 and resistor R1. The feedback loop of A1 includes resistor R4 and two antiparallel diodes D1. The output of A1 is connected at I to resistor R5 in series with antiparallel diodes D2. These are connected at point K to operational amplifier A2 with feedback resistor R2. The output of the overall circuit is provided by A2 at Vout.

A first logic circuit includes gate G1, the data input of which is connected to point I while its gate input is connected to G1 gate input. The output of G1 is connected to XOR1, the second input of which is connected to logic input X1. The XOR1 output is connected to point J common to R5 and D2 through antiparallel diodes D3. A second logic circuit G2, XOR2, D5, and D7 with logic input X2 and a G2 gate input is connected in parallel with the first logic circuit and feeds point L and M on circuit R6, D4 and R7, D6 which are respectively connected in parallel with R5 and D2. Resistor R3 is connected in parallel with the circuit between point K and Vin by closing switch SW. In this circuit, R4=R5=R6=R7=R. Digitally-Controlled One-Wave Rectifier.

If G1 gate input is set at zero logic level, the gate is closed. Therefore the output of XOR1 is only determined by the logic level on logic input X1. A one- wave rectification of the analog input signal Vin is performed either for a positive half-cycle or for a negative half-cycle. This is respectively achieved by applying to logic input X1 either -V or +V voltage level, V being the voltage drop across any one of the diodes D1...D7 which are matched. The A1, S1, R4 circuit is used only to linearize the R5, D2 transfer characteristic. The A2, R2 circuit acts as a current-to-voltage transformer. The voltage applied Vin feeds a current Iin into R1 which appears with a reversed sign in R5. D2, D3, and R5 act as s four- diode current switch.

Depending upon the sign of V applied at logic input X1, the four-diode current switch allows either a positive or negative half-cycle of Iout to flow through R2 which in turn is converted into voltage Vout by the current-to-voltage transformer. If +V is applied, Vout =(R2/R1)Vin/-/. If -V is applied, Vout = (R2/R1)Vin/+/ where Vin/-/ and Vin/+/ are, respectively, the negative and positive half-cycles of Vin. Digitally-Controlled Full-W...