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I am building an SMP series interface SOLT cal kit. Need guidance on how to extract L0,L1,L2,L3 and C0,C1,C2,C3 coefficients.

Question asked by EricBrand on Mar 9, 2018
Latest reply on Mar 24, 2018 by Dr_joel

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We have successfully built LRL/TRL calibration kits for SMPM interface per MIL-STD-348 (.069”/1.75mm airline) . This kit consists of the following: short, thru, and a 3 different lengths of airlines. With this LRL kit, we were able to get good results up to 67 GHz when we assumed zero for the L0, L1, L2, L3 coefficients for the short on the Agilent 8361C VNA. However, we are now attempting to build a SOLT calibration kit for SMP interface per MIL-STD-348. It appears that assuming zero for the L and C coefficients will not be sufficient for a good SOLT short open load thru calibration, so we are trying to figure out what the proper method of deriving/calculating L and C coefficients would be. We have looked at several papers addressing calibration methods, but each one seems to do some “hand-waving” and leave out essential details on the method of deriving L and C coefficients for the open and short. Is there any document that clearly lays out the steps necessary to derive L and C coefficients that are sufficiently accurate to work for an SOL 1-port calibration? Any guidance/direction would be highly appreciated.

Dr_joel

Mar 24, 2018 1:17 PM

Correct Answer

sorry for the delay, been travelling...

10. Change Z0 setting from 50 to 500 ohms then extract data (same data fields as above with gated smith and gated phase).

NOPE: leave it 50 ohms and measure the load, and look on the smith chart to determine impedance (should be 50 ohms, and the inductance, using markers (look at figure 9.7, lower right smith chart). take the average value of the inductance and compute the effective line delay using equation 9.4, then modifiy the load standard in the cal kit to have 500 ohms Z and the delay computed.

set your open or short up on the smith chart and use markers to pick of 3 values of capacitance across your band of interest.

Use just the values of open to get the factors for the open capacitance polynomial as in figure 9.11

Use just the values of the short to get the factors for the short inductance (or just call them zero)

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Dr_joel

Mar 13, 2018 9:03 AM

I wrote about this exact issue in Chapter 9 of my book ( http://www.wiley.com/WileyCDA/WileyTitle/productCd-1119979552.html ). The particular case was creating and evaluating PCB standards, but the methods are almost the same. Basic idea is:

Calibrate in a good type (3.5 mm). Use a high quality adapter or cable to connect to your test plane (which has your connector type). Use a short/open to get an idea of the proper reference plane. Then use gating to remove the effects of the 3.5 mm to adapter (or cable ) mismatch, or more simply, use AutoPortExtend to set the reference plane. Connect the short (I guess for this case, you just need the proper offset). For frequencies below 20 GHz, you can likely leave the L values to zero just fine. Then connect the open (it's best to use a shielded open so it does not radiate) and evaluate it's offset delay from the short, and get the phase curve. You may find the open is shorter (in distance) than the short, if you don't have an open pin extension). Use the phase curve to map to a 3rd order polynomial and get the coefficient from that.

Then evaluate the load as it appears at the reference plane, and look for the excess inductance (my experience is the load is almost always inductive, although I have seen some on-wafer standards that are in-fact capacitive). Compute the offset delay at 500 ohms to get the equivalent inductance.

Lots more details in chapter 9.

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EricBrand @ Dr_joel on Mar 13, 2018 11:07 AM

Thank you, Dr Joel. I've purchased your book and am carefully reading through Chapter 9 as you suggested. We'll be able to get some time on the VNA today to try your suggestions.

BTW... we are attempting to build a Cal Kit for SMP push-on interface up to 50 GHz.

Eric

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EricBrand @ Dr_joel on Mar 16, 2018 5:23 PM

Dr Joel.

I was able to get on the PNA and here is the procedure we followed:

1. Set up PNA 8361: ch1 time domain, ch2 phase, ch3 smith, 0.124 GHz to 50.00 GHz range.

2. Port 1 on PNA has 1.85mm(f) connection available

3. Connected adapters 2.4mm(m) to 3.5mm(m) to port 1 (since we don’t have a 1.85 to 2.4 adapter available)

4. Cal’d at 3.5mm R/P with Agilent 85052D 3.5mm cal kit (SOLT) on port 1.

5. Added 3.5mm(f) to 2.4mm(m) adapter on port 1.

6. Placed start gate at R/P of 2.4mm end of adapter. (+.80 reflection at 112 ps )

7. Placed 2.4mm Short on adapter and dialed in stop gate at *short plane*(i.e., when reflection is -1.00) (i.e., 154 ps)

8. Remove Short, then connect Open and extract data with smith gated and phase gated:

( S11 freq(Hz), UNWRAPPED S11 Phase(°), S11 SMITH Real(Ohm), S11 SMITH Imag(Ohm)

9. Disconnect Open, then connect Load.

10. Change Z0 setting from 50 to 500 ohms then extract data (same data fields as above with gated smith and gated phase).

11. Pasted data into Excel and ran 3rd degree polynomial regression on the frequency(Hz) and phase(unwrapped radians) to determine coefficients. (We’re using the Open vs Short phase curve data to get polynomial C factors for Open. And using Load vs Short phase curve data to get polynomial L factors for the Short based on our understanding of your email.

Please let us know if the above process is correct or not.

We can supply screenshots and .csv files to you if needed.

a. I suspect that we may be missing an additional step that involves translating the phase data into L and C at each frequency before we do the polynomial regression.

b. looking at the .csv output data from the PNA, I would think that

Tan(Phase(degrees)*pi()/180) = Z_imag / Z_real (per your equation 1.44 in section 1.3.2 )

But if I compare these for any given frequency, the data does not agree with this equation. Why? What are we missing here?

c. it appears that the data for the Short contains BOTH negative and positive values for Z_imag and that this would correspond to both capacitive and inductive responses at various frequencies. Should the polynomial regression to determine L factors be done on all frequencies even if Z_imag is negative at some of those frequencies?

d. it appears that the data for the Open contains BOTH negative and positive values for Z_imag and that this would correspond to both capacitive and inductive responses at various frequencies. Should the polynomial regression to determine C factors be done on all frequencies even if Z_imag is positive at some of those frequencies?

Many Thanks,

Eric Brandauer

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Dr_joel

Mar 24, 2018 1:17 PM

sorry for the delay, been travelling...

10. Change Z0 setting from 50 to 500 ohms then extract data (same data fields as above with gated smith and gated phase).

set your open or short up on the smith chart and use markers to pick of 3 values of capacitance across your band of interest.

Use just the values of open to get the factors for the open capacitance polynomial as in figure 9.11

Use just the values of the short to get the factors for the short inductance (or just call them zero)

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4 Replies

Dr_joel Mar 13, 2018 9:03 AM
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Correct Answer
I wrote about this exact issue in Chapter 9 of my book ( http://www.wiley.com/WileyCDA/WileyTitle/productCd-1119979552.html ). The particular case was creating and evaluating PCB standards, but the methods are almost the same. Basic idea is:

Calibrate in a good type (3.5 mm). Use a high quality adapter or cable to connect to your test plane (which has your connector type). Use a short/open to get an idea of the proper reference plane. Then use gating to remove the effects of the 3.5 mm to adapter (or cable ) mismatch, or more simply, use AutoPortExtend to set the reference plane. Connect the short (I guess for this case, you just need the proper offset). For frequencies below 20 GHz, you can likely leave the L values to zero just fine. Then connect the open (it's best to use a shielded open so it does not radiate) and evaluate it's offset delay from the short, and get the phase curve. You may find the open is shorter (in distance) than the short, if you don't have an open pin extension). Use the phase curve to map to a 3rd order polynomial and get the coefficient from that.

Then evaluate the load as it appears at the reference plane, and look for the excess inductance (my experience is the load is almost always inductive, although I have seen some on-wafer standards that are in-fact capacitive). Compute the offset delay at 500 ohms to get the equivalent inductance.

Lots more details in chapter 9.
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- EricBrand @ Dr_joel on Mar 13, 2018 11:07 AM
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  Thank you, Dr Joel. I've purchased your book and am carefully reading through Chapter 9 as you suggested. We'll be able to get some time on the VNA today to try your suggestions.
  BTW... we are attempting to build a Cal Kit for SMP push-on interface up to 50 GHz.
  
  Eric
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- EricBrand @ Dr_joel on Mar 16, 2018 5:23 PM
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  Correct Answer
  Dr Joel.
  
  I was able to get on the PNA and here is the procedure we followed:
  1. Set up PNA 8361: ch1 time domain, ch2 phase, ch3 smith, 0.124 GHz to 50.00 GHz range.
  2. Port 1 on PNA has 1.85mm(f) connection available
  3. Connected adapters 2.4mm(m) to 3.5mm(m) to port 1 (since we don’t have a 1.85 to 2.4 adapter available)
  4. Cal’d at 3.5mm R/P with Agilent 85052D 3.5mm cal kit (SOLT) on port 1.
  5. Added 3.5mm(f) to 2.4mm(m) adapter on port 1.
  6. Placed start gate at R/P of 2.4mm end of adapter. (+.80 reflection at 112 ps )
  7. Placed 2.4mm Short on adapter and dialed in stop gate at *short plane*(i.e., when reflection is -1.00) (i.e., 154 ps)
  8. Remove Short, then connect Open and extract data with smith gated and phase gated:
  ( S11 freq(Hz), UNWRAPPED S11 Phase(°), S11 SMITH Real(Ohm), S11 SMITH Imag(Ohm)
  
  9. Disconnect Open, then connect Load.
  
  10. Change Z0 setting from 50 to 500 ohms then extract data (same data fields as above with gated smith and gated phase).
  
  11. Pasted data into Excel and ran 3rd degree polynomial regression on the frequency(Hz) and phase(unwrapped radians) to determine coefficients. (We’re using the Open vs Short phase curve data to get polynomial C factors for Open. And using Load vs Short phase curve data to get polynomial L factors for the Short based on our understanding of your email.
  
  Please let us know if the above process is correct or not.
  
  We can supply screenshots and .csv files to you if needed.
  
  a. I suspect that we may be missing an additional step that involves translating the phase data into L and C at each frequency before we do the polynomial regression.
  
  b. looking at the .csv output data from the PNA, I would think that
  Tan(Phase(degrees)*pi()/180) = Z_imag / Z_real (per your equation 1.44 in section 1.3.2 )
  But if I compare these for any given frequency, the data does not agree with this equation. Why? What are we missing here?
  
  c. it appears that the data for the Short contains BOTH negative and positive values for Z_imag and that this would correspond to both capacitive and inductive responses at various frequencies. Should the polynomial regression to determine L factors be done on all frequencies even if Z_imag is negative at some of those frequencies?
  
  d. it appears that the data for the Open contains BOTH negative and positive values for Z_imag and that this would correspond to both capacitive and inductive responses at various frequencies. Should the polynomial regression to determine C factors be done on all frequencies even if Z_imag is positive at some of those frequencies?
  
  Many Thanks,
  
  Eric Brandauer
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Dr_joel Mar 24, 2018 1:17 PM
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Correct Answer
sorry for the delay, been travelling...

10. Change Z0 setting from 50 to 500 ohms then extract data (same data fields as above with gated smith and gated phase).

NOPE: leave it 50 ohms and measure the load, and look on the smith chart to determine impedance (should be 50 ohms, and the inductance, using markers (look at figure 9.7, lower right smith chart). take the average value of the inductance and compute the effective line delay using equation 9.4, then modifiy the load standard in the cal kit to have 500 ohms Z and the delay computed.

set your open or short up on the smith chart and use markers to pick of 3 values of capacitance across your band of interest.
Use just the values of open to get the factors for the open capacitance polynomial as in figure 9.11
Use just the values of the short to get the factors for the short inductance (or just call them zero)
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I am building an SMP series interface SOLT cal kit. Need guidance on how to extract L0,L1,L2,L3 and C0,C1,C2,C3 coefficients.

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