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Chapter 4 Theory of Operation
A-to-D Converter
A-to-D Converter
Referring to the schematic shown on page 129, the
The ADC method used by the Agilent E3631A is called multislope III. Multislope III is a charge balancing continuously integrating
Switch U5 steers fixed positive or negative reference currents onto the integrator capacitors to cancel, or balance the accumulated input charge. The level shifted (R19 and R20 on the top board) output of the integrator is checked every 2.66 mA by the U16 COMP input. Logic state machines in U16 control the U5 current steering to continuously seek an approximate 2.5 V level on the integrator amplifier output, FLASH. If the ADC input voltage ADC REF is between ±15 V, the integrator output (FLASH) will remain within the 0 V to 5 V range of the U17
The integrator amplifier is formed by U6 and U8. Resistors R10 and R11 affect the amplifier stability. Amplifier oscillation may occur if their values are incorrect. Amplifier U6 improves the offset voltage characteristics of integrator amplifier U8 on the top board.
Each
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