JAJSIB3D August 2017 – February 2021 THS4561
PRODUCTION DATA
The circuit of Figure 8-5 is a typical setup for common-mode measurements.
In Figure 8-5, the differential path is terminated back to ground with the two 1.5-kΩ input resistors and the VOCM control input is driven from a 50-Ω matched source for the frequency response and step response curves of Figure 7-47, Figure 7-49, and Figure 7-50. The outputs are summed to a center point (to obtain the average, or common-mode output, VOCM) through two 100-Ω resistors. These 100-Ω resistors form an equivalent 50-Ω source to the common-mode output for measurements. Figure 7-48 illustrates the common-mode output noise measurements with a ground on the VOCM input pin or with the VOCM input pin floating. The higher noise in Figure 7-48 for a floated input can be reduced by including a capacitor to ground at the VOCM control input pin.