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Shared Nonlinear Reference Source for A/D and D/A Conversion

IP.com Disclosure Number: IPCOM000083979D
Original Publication Date: 1975-Aug-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 2 page(s) / 71K

Publishing Venue

IBM

Related People

Schindler, HR: AUTHOR [+3]

Abstract

A source for nonlinear reference signal is described which can be shared by a plurality of analog-to-digital (A-to-D) converters, of the type in which the unknown signal is compared to a periodic time-varying reference signal, and the time between start and coincidence is counted to generate the digital representation. It is also suitable for digital-to-analog (D-to-A) conversion.

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Shared Nonlinear Reference Source for A/D and D/A Conversion

A source for nonlinear reference signal is described which can be shared by a plurality of analog-to-digital (A-to-D) converters, of the type in which the unknown signal is compared to a periodic time-varying reference signal, and the time between start and coincidence is counted to generate the digital representation. It is also suitable for digital-to-analog (D-to-A) conversion.

To provide a nonlinear companded conversion characteristic as suggested by CCITT (recommendations G. 711), a reference signal as shown in Fig. 1 is generated. It consists of 13 linear sections.

The sampling interval is subdivided into 20 equal intervals, 16 for the conversion period and 4 for the resetting as indicated in Fig. 1.

The signal is generated by integrating binary weighted currents.

Fig. 2 shows a block diagram of the nonlinear reference source. It comprises: seven current sources in the form of a resistor network R, 2R, 4R, 8R, 16R, 32R and 64R providing currents I, I/2, I/4, I/8, I/16, I/32, I/64; control logic to switch the current sources individually to a common line L; and an integrator circuit.

A further current source is provided for furnishing a reset current I of opposite direction, which can also be switched by the control logic.

The control logic has a cyclic program such that the resultant integrator input current on line L has the following sequence: Time Interval Current Time Interval Current No. (in...