ZHCSCX2E January 2014 – October 2017 LM15851
PRODUCTION DATA.
A differential input signal must be used to drive the LM15851device. Operation with a single-ended signal is not recommended as performance suffers. The input signals can be either be AC coupled or DC coupled. The analog inputs are internally connected to the VCMO bias voltage. When DC-coupled input signals are used, the common mode voltage of the applied signal must meet the device Input common mode requirements. See VCMI in the Recommended Operating Conditions table.
The full-scale input range for each converter can be adjusted through the serial interface. See the Full Scale Range Adjust section.
The buffered analog inputs simplify the task of driving these inputs and the RC pole that is generally used at sampling ADC inputs is not required. If an amplifier circuit before the ADC is desired, use care when selecting an amplifier with adequate noise and distortion performance and adequate gain at the frequencies used for the application. If gain is not required, a balun (balanced-to-unbalanced transformer) is generally used to provide single ended (SE) to differential conversion.
The input impedance of VIN± consists of two 50-Ω resistors in series between the inputs and a capacitance from each of these inputs to ground. A resistance of approximately 20 kΩ exists from the center point of the 50-Ω resistors to the on-chip VCMO providing self-biasing for AC-coupled applications.
Performance is good in both DC-coupled mode and AC coupled mode, provided the common-mode voltage at the analog input is within specifications.