ICCAP Project

1
ICCAP Project

• Wk 11

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ICCAP

• ICCAP Integrated Circuit Characterization Program
  by Agilent Technologies
• Used in Junior Lab along with A5631 DC Source
  Monitor to DC characterize BJT,s and FETs.
• Can also be used with microwave network analyzer
  to extract device capacitance model.

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2 port circuit models

• Two port circuit model relate voltages and
  currents of two pairs of terminals in a 2x2
  matrix form. Current into the ports is considered
  positive. Usually one of the two terminals at
  each port is considered grounded.
• Various forms are possible depending on how the
  voltages and currents are arranged. The include
  Z, Y, H, G, T, and S parameter form.

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Two port impedance Z parameters

• The two port Z parameter equations are
• Z11 and Z22 can be obtained by applying a source
  to a port with the opposite port open circuit
  making that that port current zero.
• Z12 and Z21 can be obtained by applying a forced
  current to a terminal pair and measuring the
  opposite terminal open circuit voltage.

5
Two port admittance Y parameters

• The two port admittance equations are
• Y11 and Y22 can be obtained by applying a source
  to a port with the opposite port short circuited
  making that port voltage zero.
• Y12 and Y21 can be obtained by applying a forced
  voltage to a terminal pair and measuring the
  opposite terminal short circuit current. (Note I
  positive into terminal).

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FET two port admittance Y parameters

• FET Y parameters have a PI shaped capacitor
  arrangement Cgs, Cgd, Cds with a transconductance
  voltage dependant current source in parallel with
  Cds.
• The Y parameter matrix is then
• Measured AC data can be used to find Cgd from
  Y12. Then Cgs can be found from Cgd and Y11. Cds
  can be found from Y22 abd Cgd. Lastly gm can be
  found from the real part of Y21.

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H and ABCD parameters

• Less common are the H parameters used for BJTs
  where H21 (also called hfe) is beta
• The ABCD parameters solve port to port connection
  by taking the matrix product in ABCD form.

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Parallel and Series Two Port

• Parallel two port connection connects the same
  port pins of two circuits together. Parallel
  connected two port admittance matrices add.
• Series two port connection connects the upper
  port 1 of one circuit to the lower port 1 pin of
  the second circuit and the upper port 2 of the
  first circuit to the lower port two of the second
  circuit. Series connected two port impedance
  matrices add.

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S parameters

• Microwave network analyzers measure the
  transmitted and reflected power waves of a
  circuit referred to as the S parameters.
• The S parameters are complex numbers with
  magnitude and phase.
• The reflection and transmission depend on the
  impedance of the transmission lines (cables)
  involved usually 50 ohms.
• The S parameters can be converted to Y or Z
  parameters if the transmission line impedance is
  known.

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S to Y parameter conversion

• The Y admittance matrix in terms of S parameters
  is given as
• ICCAP directly controls the network analyzer to
  get the s parameters and has built in software
  for s to Y or Z conversion and Y to Z or Z to Y
  conversion.

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Deembedding

• Network analyzer measurement relies on
  calibration to know standards that fix the
  reference locations pr planes.
• Additional transmission line, parasitic
  inductance, capacitance, and resistance occur
  between the reference plane and the device.
• A circuit with a transmission line between the
  reference planes, another circuit without a
  device, and another with a shorted replacing the
  device can be used to measure the parasitic
  elements.
• Once the transmission line and parasitic element
  values are known they can be removed by
  deembedding.
• The transmission line is removed by
  multiplication in the s parameter domain.

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Deembedding 2

• S parameters are converted to Z parameters.
• Known parasitic series inductance and resistance
  are removed in the Z domain by subtraction.
• The remaining Z parameters are converted to Y
  parameters.
• Known parasitic capacitors in parallel connection
  are removed by subtracting Y matrices.
• The remaining intrinsic device Y parameters are
  then used to extract the device parameters Cgs,
  Cgd, Cds, gm, etc. depending on the device model.