1. LM98640 S11 Parameter Extraction
Supplied by Kirby Kruckmeyer
Compiled September 9, 2009

2. Input Network of the LM98640
The input of the LM98640 consists of switches and capacitors. The input network is configured differently in different phases of the operations. During sample phase, the switches are turned on so the equivalent circuit is the sampling capacitor in series with the resistance provided by the switches. The total capacitance including the sampling capacitor and parasitic is about 7.5pF when CDS gain is disabled (also known as cds1x mode, please refer to bit<2> in the main configuration register). The total capacitance is about 13.2pF when CDS gain is enabled (also known as cds2x mode). During hold phase, the switches are turned off so it behaves like an open circuit. This is the case for both S/H mode and CDS mode.

3. Input Network of the LM98640
In correlated double sampling (CDS) mode, the input networks exhibit same electric characteristic during the clamp phase (when the reference level of the CCD waveform is sampled) and the sample phase (when the video level is sampled). As a result, the S parameter for the sample phase also applies to the clamp phase in correlated double sampling mode.

4. Typical S11 in CDS 1x Gain Mode

5. Typical S11 in CDS 2x Gain Mode

6. S11 in S/H Mode CDS 1X gain sample phase CDS 1X gain hold phase

7. S11 in Correlated Double Sampling Mode
CDS 1X gain samp/clamp phase
CDS 1X gain hold phase
CDS 2X gain samp/clamp phase
CDS 2X gain hold phase