For an On Wafer setup, how do I improve my smith chart coverage?

June 12, 2024


Category: FDCS On-wafer measurements

Symptoms / Solutions:

For an on-wafer setup, the maximum smith chart coverage that can be achieved by the tuner is affected by the insertion loss between the tuner and the DUT reference plane. In most cases, the insertion loss comes from the on-wafer probe and the cable between the on-wafer probe and tuner as shown in the following figure.

Figure 1: Common on-wafer setup with load tuner

The gamma at the DUT reference plane can be expressed as:

where Γtuner is the gamma presented by the tuner itself, S11, S12,S21 and S22 are the S-parameter of the probe & cable.

From (1), to improve the smith chart coverage, it is recommended to use low insertion loss probe and cable.

Additional Information:

To preview the gamma at the DUT reference plane with different insertion loss and tuner gamma, RF Calculator in the Utilities can be used as shown in Figure 2.

Figure 2: VSWR/Loss utility

Keywords: On-wafer, tuner, coverage, maximum gamma

Last date modified:  2017/05/02