a confusion in LT5560 0.01MHz to 4GHz Mixer datasheet

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yyan71

Joined: 24 Sep 2009
Posts: 7
Location: Australia

05 Nov 2009 3:08 a confusion in LT5560 0.01MHz to 4GHz Mixer datasheet

Hi there, I'm confused in understanding about how to determine the source impedance of the input port of LT5560, which is on page 16 of its datasheet.

It says the input transformer has a 1:1 impedance ratio, so Rs = 50ohms. However, according to Figure 5, the RL = 28.1ohms. If impedance ratio is 1:1, I think Rs is 50ohms. Confused....

The screen cut of the relative page has been attached. Key words have been highlighted.

The whole datasheet can be found here:
http://www.farnell.com/datasheets/72197.pdf

Please help me... [img][/img][/img]

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Mazz

Joined: 03 Nov 2001
Posts: 592
Helped: 80

05 Nov 2009 7:50 a confusion in LT5560 0.01MHz to 4GHz Mixer datasheet

The answer is not so difficult: the 28 load impedance is matched to 50 Ohm source impedance through the LC matching network.
L is splitted into an internal part (you cannot act on it) and an external tunable part, depending on frequency usage.
Once you have transformed internal impedance at a certan freq to 50 Ohm differential, then you use an 1:1 transformer to convert it into single ended 50 Ohm.

I hope it can help.

Mazz