Circuit Cellar Contest - RF Transponder

Joerg wrote:
> Looks like the IF filter to me, with L1/C4 doing the phase shift for the
> diff input.

Yes, you are right.  It's a filter, not a crystal.

> Who knows why they decided to design the TRF with a
> differential IF input, doesn't make a lot of sense to me. Infineon
> didn't do that on the TDA5210.

Perhaps for noise margins with lower VCC (2.2V to 3.6V for TRF vs. 5V
for the TDA).  Anyway, I am not going to worry about the physical size,
except with the note: "smaller board can be made".   The lower VCC is
swinging me back into the TRF camp for now.

By the way, what would be good choices for RF Amps?  It will be feeding
directional antenna if output exceeds FCC limits.

> 
> -- 
> Regards, Joerg
> 
> http://www.analogconsultants.com

Hello Linnix,


>>Looks like the IF filter to me, with L1/C4 doing the phase shift for the
>>diff input.
> 
> Yes, you are right.  It's a filter, not a crystal.
> 
>>Who knows why they decided to design the TRF with a
>>differential IF input, doesn't make a lot of sense to me. Infineon
>>didn't do that on the TDA5210.
> 
> Perhaps for noise margins with lower VCC (2.2V to 3.6V for TRF vs. 5V
> for the TDA).  Anyway, I am not going to worry about the physical size,
> except with the note: "smaller board can be made".   The lower VCC is
> swinging me back into the TRF camp for now.
> 

Again, check NordicSemi as well:

http://www.nordicsemi.com/index.cfm?obj=product&act=display&pro=83


> By the way, what would be good choices for RF Amps?  It will be feeding
> directional antenna if output exceeds FCC limits.
> 

Don't know, I used to do them discrete. Picked a nice transistor and had 
at it. But this is not cool if you need pre-cert stuff.

-- 
Regards, Joerg

http://www.analogconsultants.com