two questions to RF converters

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#1
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Hi,

Recently I've been reading articles about RF converters and have two questions to the parameters.

1. IIP3 or OIP3
Is it correct, that for upconverters OIP3 is critical and for downconverters IIP3 is critical?

2. 1dB Compresssion
I have seen a -6dB for a converter and a +5dB for another converter. Should this compression be positive or negative? Or it depends on if it is an upconverter or a downconverter?

Senmeis

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Not sure why one intercept point is more "important" for up or down converters.

On second, are you sure that the quoted levels are not dbm rather than db? If it really is, then +5dbm means that the converter will work with a stronger input signal before compressing than -6dbm one. In fact the first works with 11db higher amplitude input before compressing by 1db.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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1) Perhaps if you quoted some typical examples you might get some suggestions.

In an up-conversion system you may be less concerned with the image frequency, LO rejection, image noise and this might permit a higher OIP3 level than in a down-conversion system.

Getting rid of the image and 1/2IF responses were driving factors for an up-conversion solution to a multi-band PMR radio. However, I do not recall that we focussed on IIP3 versus OIP3.

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Please follow these links:

http://www.hittite.com/products/...
http://www.hittite.com/products/...

You will see IIP3 is only relevant to downconverters and OIP3 is only relevant to upconverters.

For the second question, sorry, it should be dBm, but it seems that the 1dB compression is positive for upconverters and negative for downconverters. At least this characteristic can be seen from the data sheets above.

Senmeis

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I think the key words are and
.

The down converters are for receiver applications and I believe RX guys think more in terms of IIP3, whereas us transmitter guys are more interested in the OIP3 levels.

For the second comment, I would have to look through all the relevant datasheets, but my guess is similar to my first comment ... these downconverters are aimed at lower signal level receiver applications and the upconverters are aimed at higher signal level transmit applications.

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Drawing a general conclusion such as:

Quote:
You will see IIP3 is only relevant to downconverters and OIP3 is only relevant to upconverters
from a single manufacturer or a small number of data sheets is dangerous. You may well get different conclusions from Analog Devices.

Those conclusions may also be technology dependent. Hittite has a specific technology. They are very good at what they do. But, I would never draw such a conclusion about general hardware based on one source.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Thank you.

Senmeis