Texas Instruments CC11XX 50 Ohm question

Hi,

I noticed that none of the CC11XX chips made by Texas has a 50 Ohm output impedance.

When reading the datasheet I find something like "Optimum Load Impedance 55 + j25"

I actually can't find "Output impedance = 50 Ohm"

Are there any specific reasons?


Thanks,
Enrico Migliore

it could be to make the inductor part of the output matching network, off the chip, saves area and cost. You then have to provide it?
Frank

Very few RF chip have 50 Ohm output impedance. Some have specified data measured at 50 Ohm.
All CC11xx are, as far as I know, complementary output where each port is a kind of current source. Complementary is not equal to differential.
For best performance must output matching then also provide a kind tank circuit or a real transformer if antenna is unbalanced.
Simplest is to very closely follow an application example and then only do minor adjustments to make antenna impedance fit.
Check TI forum, it is full of designs whit performance related problems due to less good impedance matching and due to this, also problems with harmonics.
It is not unique for TI, many other brands of modern RF chips are designed in a similar way.

Hi,

thank you for your answer.

> Very few RF chip have 50 Ohm output impedance. Some have specified data measured at 50 Ohm.
> All CC11xx are, as far as I know, complementary output where each port is a kind of current source. Complementary is not equal to differential.
> For best performance must output matching then also provide a kind tank circuit or a real transformer if antenna is unbalanced.
> Simplest is to very closely follow an application example and then only do minor adjustments to make antenna impedance fit.
> Check TI forum, it is full of designs whit performance related problems due to less good impedance matching and due to this, also problems with harmonics.
> It is not unique for TI, many other brands of modern RF chips are designed in a similar way.

I'm not a native English speaker.

Could you write your answer in simpler words?

Thank you,
Enrico Migliore

I am neither native English spoken.
Is Google translate understandable?

Generally speaking, I don't know any RF transmitter chips, either with differential or single ended output that expose a 50 ohm real impedance. In so far the question isn't specific to Chipcon/TI chips, I think.

Talking about "CC11XX chip" is unclear in particularly, because some have single ended outputs, most recent transceiver chips like CCC1101 have differential ones.

The point is, you'll need a matching network for any transmitter or transceiver chip from the market, for differential ended outputs, you need a balun, too.