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Sunday, October 18, 2009

Auto Ranging Circuit Using LTCxxxx IC

This is a circuit that is the name called auto ranging circuit. This circuit is useful to extend the measurement range of an available ADC (analog-to-digital converter). The circuit will best implemented for multiplexed input. LTC1257 is appropriate for system auto ranging, adjusting an ADC’s full-scale range. This is the picture of the schematic.

This circuit is use IC with LTC type. During the conversion process, U2 and U3 receive the full and zero scale codes, respectively, that correspond to a selected multiplexer channel. For example, let channel 2’s span begin at 2V and end at 4.5V. When a host processor wants a conversion of channel 2’s input signal, it first sends code that sets the output of U2 to 2V and U3 to 4.5V, fixing the span to 2.5V. The processor then sends data to the LTC1296 selecting channel 2. The processor next clocks the LTC1296 and reads the data generated during the conversion of the 3.5VP-P signal applied to channel 2. As other multiplexer channels are selected the DAC outputs are changed to match their spans.

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