9042 Datasheet, PDF (20/26 Pages) Maxwell Technologies – 12-Bit, 41 MSPS A/D Converter

12-Bit, 41 MSPS A/D Converter
9042
As a final alternative, the ECL gate may be replaced by an ECL comparator. The input to the comparator could then be
a logic signal or a sine signal.
Figure 25. ECL Comparator for Encode
Care should be taken not to overdrive the encode input pin when ac coupled. Although the input circuitry is electrically
protected from over or under voltage conditions, improper circuit operations may result from overdriving the encode
input pins.
Driving the Analog Input
Because the 9042 operates off of a single +5 V supply, the analog input range is offset from ground by 2.4 volts. The
analog input, AIN, is an operational amplifier configured in an inverting mode (ref. Equivalent Circuits: Analog Input
Stage). VOFFSET is the noninverting input which is normally tied through a 50 ohm resistor to VREF (ref. Equivalent
Circuits: 2.4 V Reference). Since the operational amplifier forces its inputs to the same voltage, the inverting input is
also at 2.4 volts. Therefore, the analog input has a Thevenin equivalent of 250 ohms in series with a 2.4 volt source. It
is strongly recommended that the 9042’s internal voltage reference be used for the amplifier offset; this reference is
designed to track internal circuit shifts over temperature.
01.07.05 REV 7
All data sheets are subject to change without notice 20
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