SLWS214C October 2008 – May 2026 ADS61B29 , ADS61B49
PRODUCTION DATA
The analog input consists of an integrated input buffer followed by a switched-capacitor based differential sample and hold architecture. The addition of a buffer provides isolation from the non-linear impedance and switching transients of the switched-capacitor circuit. With a constant input impedance, the ADC is easier to drive and to reproduce data sheet measurements. For wide-band applications, like power amplifier linearization, the signal gain across frequency is more consistent. Spectral performance variance across frequency is also reduced.
This differential topology results in very good ac performance even for high input frequencies at high sampling rates. The INP and INM pins have to be externally biased around a common-mode voltage of 2.3 V, available on the VCM pin. For a full-scale differential input, each input pin INP, INM has to swing symmetrically between VCM+ 0.5 V and VCM – 0.5 V, resulting in a 2-Vpp differential input swing.
Figure 7-1 Analog Input Equivalent CircuitThe input sampling circuit has a high 3-dB bandwidth that extends up to 750 MHz (measured from the input pins to the sampled voltage).