how to get these values?
333 6
redsunwit 3 months ago
hello, i am using LT5560 right now. i try to design the match circuit. from the instruction of LT5560, i get the following table. i want to get the imput impedance for frequency at 910MHz, but this frequency does not show up in the following table. i wonder how to get this value? ![Screenshot from 2019-06-08 21-42-50.png](//image.easyeda.com/pullimage/qYeyRkyLzcy6kdysnqba6jCAL8RswjdNqY5oBYwR.png)
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andyfierman 3 months ago
Given the component tolerances in the matching circuit, you should be OK using the 900MHz values. To get better than that you could try curve fitting the table and interpolating up from 900MHz. Or try using: [https://www.analog.com/en/products/lt5560.html#product-tools](https://www.analog.com/en/products/lt5560.html#product-tools) although it doesn't look like it runs very well on WINE: [https://appdb.winehq.org/objectManager.php?sClass=application&iId=9347](https://appdb.winehq.org/objectManager.php?sClass=application&iId=9347) Do you have suitable test equipment with which to measure the circuit performance?
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redsunwit 3 months ago
Thanks for answering my question and your patience. 1\. actually\, i don't have any test equipments to measure the circuit performance right now\. 2\. from LT5560\, we can see that we use L \-style matching circuit for MHz signals\.   but\, for Khz signals \(450KHz output signals\)\, there is a different matching circuit as follows: it seems that the output impedance matching circuit is not a standard L-style matching circuit. what if i want to design an INPUT matching circuit for KHz signals? can i just use the following output matching circuit with modifying its parameters? ![Screen Shot 2019-06-09 at 15.36.37.png](//image.easyeda.com/pullimage/dUaozvjY3aU9obDbwKI0cc7yvIH79cU2GGofpVST.png)
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andyfierman 3 months ago
The LT5560 is not specified for operation below an input frequency 10MHz. You'll need to look carefully at the datasheet to get some clues about how to use it below that. Look closely at the Pin Functions descriptions for the IN+/- pins and at Figure 5.
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redsunwit 3 months ago
@andyfierman yes, it does not specify when the input frequency is below 10MHz. but LT5560 does works for 0.01MHz to 4GHz. I guess i have to figure it out by myself. Thanks a lot for your replying.
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andyfierman 3 months ago
Sorry, I'm being stupid. That's 10kHz! I was reading 0.01GHz instead of 0.01MHz. Down at 450kHz as long as you can provide a low source resistance to ground to meet the input current requirements, you can probably just drive it with the output of a pair of opamps set up to give a differential output. You don't care too much at such low frequencies as transmission line effects and impedance matching won't affect things unless you are driving the input from a very long cable or a tuned circuit.
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redsunwit 3 months ago
@andyfierman  got it. Thanks, my friend. have a great day
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