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7rots51
Joined: 17 May 2002
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 28 Jun 2008 21:10 SA636 input matching |
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How to design input matching of SA636 for 374MHZ (50 ohm) RF input signal?
How to calculate L,C values?
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RF-OM
Joined: 03 Aug 2007
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| 28 Jun 2008 22:59 Re: SA636 input matching |
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| You need to know Z=R+iX input impedance for this frequency or S-parameter file for the device. When Z is known it is easy, just use any good matching calculator. if you have no one , send me your Z complex number and I will calculate it for you. With S-parameter file it is a bit more complicate because S-parameters may be measured for different frequencies, therefore interpolation will involved.
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boy
Joined: 30 Sep 2002
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| 29 Jun 2008 5:40 SA636 input matching |
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From the datasheet Zin = 700+ 3.5pf = 700 - j*121.58 at 374 MHz then use a matching tool such as WinSmith to design a matching network.
http://mrtmag.com/mag/radio_winsmith_computerized_smith/
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RF-OM
Joined: 03 Aug 2007
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| 30 Jun 2008 18:46 Re: SA636 input matching |
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| Okay. You may match 700-j121.58 impedance to pure 50 Ohm with lowpass LC circuit (series L=77.95 nH and then shunt C=2.06 pF) or with high pass circuit (series C=2.32 pF and then shunt L=79.97 nH).
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VSWR
Joined: 07 Feb 2002
Posts: 618
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| 30 Jun 2008 23:22 Re: SA636 input matching |
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Not quite. The input impedance of the SA636 is 700 ohms, having a parallel (not series) capacitance of 3.5 pF. Matching of this load would be the following:
Source (50 ohms) --> 2.2 pF series capacitor --> 33 nH parallel inductor --> SA636 input (load)
(rounded values)
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RF-OM
Joined: 03 Aug 2007
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| 01 Jul 2008 5:40 Re: SA636 input matching |
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Well. 700 Ohm and 3.5 pF parallel cap will correspond to 20.5-j118.02 impedance. To match pure 50 Ohm source with this impedance 4 different circuits can be used. High pass LC 2.36 series cap and 31.81 nH shunt L; low pass 10.21 shunt C and series 60.69 nH inductor. Two other circuits have two inductors and therefore are not so interesting.
Boy provided 700-j121.58 Ohm impedance and this means series form, not parallel. I was surprised a bit high resistive part (700 Ohm), but calculate match for given by boy number.
Matching calculations as well as conversion from parallel to series form were done with LINC2 matching calculator.
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boy
Joined: 30 Sep 2002
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| 01 Jul 2008 12:10 Re: SA636 input matching |
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| RF-OM wrote: |
Well. 700 Ohm and 3.5 pF parallel cap will correspond to 20.5-j118.02 impedance. To match pure 50 Ohm source with this impedance 4 different circuits can be used. High pass LC 2.36 series cap and 31.81 nH shunt L; low pass 10.21 shunt C and series 60.69 nH inductor. Two other circuits have two inductors and therefore are not so interesting.
Boy provided 700-j121.58 Ohm impedance and this means series form, not parallel. I was surprised a bit high resistive part (700 Ohm), but calculate match for given by boy number.
Matching calculations as well as conversion from parallel to series form were done with LINC2 matching calculator. |
That is right. It is parallel. Sorry about that
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7rots51
Joined: 17 May 2002
Posts: 1261
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| 09 Jul 2008 14:08 Re: SA636 input matching |
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But the values given in datasheet is for 240MHZ ,how you use it for 374MHZ?
Is this possible?
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RF-OM
Joined: 03 Aug 2007
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| 09 Jul 2008 18:26 Re: SA636 input matching |
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| You gave me the frequency and impedance, I used your data. Why I should check everything? If you want to have right answer you need to be careful enough to get it.
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VSWR
Joined: 07 Feb 2002
Posts: 618
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| 10 Jul 2008 11:38 Re: SA636 input matching |
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7rots51,
The input impedance of the SA636 is 700 ohms, having a parallel capacitance of 3.5 pF. This data is given in the data sheet, see below.
This means the input circuit of the SA636 can be matched to virtually any frequency (below the SA636 maximum input frequency of 500 MHz), using a single capacitor and inductor. Component values are calculated using the Smith chart.
The example given for 240 MHz in fig 9 in the data sheet uses the same type of matching, but the component values are selected for matching at 240 MHz.
Do you see the difference?
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