SLUAAI3 January   2022 TPS62810-Q1 , TPS62811-Q1 , TPS62812-Q1 , TPS62813-Q1 , TPS62816-Q1 , TPS628501 , TPS628501-Q1 , TPS628502 , TPS628502-Q1 , TPS628503 , TPS628503-Q1 , TPS628510 , TPS628511 , TPS628512 , TPS62870 , TPS62870-Q1 , TPS62871 , TPS62871-Q1 , TPS62872 , TPS62872-Q1 , TPS62873 , TPS62873-Q1 , TPS62874-Q1 , TPS62875-Q1 , TPS62876-Q1 , TPS62877-Q1 , TPS62A01 , TPS62A01A , TPS62A02 , TPS62A02A , TPS62A06 , TPS62A06A , TPSM82810 , TPSM82813 , TPSM8287A06 , TPSM8287A10 , TPSM8287A12 , TPSM8287A15

 

  1.   Trademarks
  2. 1Introduction
  3. 22-Port Shunt-Through Measurement Theory
  4. 3System Setup and Calibration Elements
  5. 42-Port Shunt-Through Measurement of the TPS62A01 Output PDN
  6. 5PDN Impedance Measurement Example
  7. 6Summary
  8. 7References

2-Port Shunt-Through Measurement Theory

Figure 2-1 2-Port Shunt-Through Circuit Configuration

Figure 2-1 shows the 2-Port Shunt-Through circuit configuration to measure Z 1 impedance. First of all, the S-parameter S 2 1 is calculated to derive the Z 1 impedance value. As per definition, S 2 1 is:

Equation 1. S21=V2+I2R0V1+I1R0=2 Z12 Z1+R0

Assuming that R0= 50 Ω and S21<< 1 (for very small impedance / resistances - Z1<< R0) when solving for Z1, the result is:

Equation 2. Z1=25 S211-S21~25 S21

It is important to note that the measure of S21is influenced by the VNA performance such as the dynamic range, the signal-to-noise ratio and the effective number of bits.

As all grounds in a VNA refer to the same point, an additional common mode current is created and affects measurement accuracy resulting in measurement errors. A Semi-floating differential amplifier is then used as a ground isolator to minimize ground loop currents.

Figure 2-2 2-Port Shunt-Through Circuit Configuration

Figure 2-2 shows a 2-port shunt-through measurement setup. The 2-port shunt-through measurement uses a vector network analyzer (VNA) to compute impedances at very high frequency and a semi-floating differential amplifier to measure impedances down to 1 mΩ. Selecting a semi-floating differential amplifier with a large resistance to common mode current is paramount to improve the accuracy of the measurements especially at lower frequencies.