Can I jump over this internal IF Filter?
in TDA7000 FM Radio IC
its datasheet is here:
http://www.semiconductors.philips.co...7000_CNV_2.pdf
Can I neglect the IF filter and replace it with another external higher BW one by shorting pins 9 and 12 together?
I want to use the TDA7000 in digital data link with high bit rate,but i think that i am limited with the narrow band IF filter (which is maximum of 7.5KHz...
Anysuggestions?!?!?!
Best Regards and thanks in advance,
Ahmad,
Probably not. Both of those nodes are driven by an amplifier stage. Their outputs will be fighting each other.
If you do not mind risking the damaging of an IC, try it on one.
Okay, what about connecting pin7 or 8 to 12 or 11 instead of the above? And i can't understand what is the problem with connecting that two amplified points?!?!
Can't i find a solution (not risky)
I have only one IC right now, then, i am afraid that i get it damaged..
Can't i make it via simulation? I don't have a model for it, can anyone help me to build a model for it?
Thanks in advance,
pin 8 to 12 looks less risky. These are high impedance points. One problem you will face is that the internal filter will still be there.
Try pin 7 to 12 and then put a a large capacitor from pin 8 to ground to keep the signal from that path.
Your best bet is to put your filter and an extra amplifier in the external path from pins to 12.
Yes, You're right, I think that short circuiting pins 7 to 12 may be better than from 8 to 12 but if i understood why did we put that large cap!,
but about adding the filter, isn't there any constrains on that filter gain or anything like that? i.e. altohough i made my own path overriding the IF filter, but the filter path still exists, then, will both signals interfere together? or what?
But i didn't understand this:
What will this cap do?
Think in it with me please,
Thanks alot for your help,
Ahmad,
Shorting this pin with a capacitor to ground will keep the signals from going through the internal IF filter path and adding to your external filter path. This will produce a strange IF bandpass with a higher gain in the center part compared to the edge parts.
And why would you not just change the values of C10 and C11 for the wider bandwidth you wish?
http://www.inthelight.co.nz/electronics/tda7000.htm is a good site with links to the data sheet and application notes which describe changing the IF bandwidth..
The internal filter has poor shape factor is one reason for an external filter.
When I said earlier to connect nodes together, I meant using a capacitor. These notes might have different DC bias conditions.
I'm sorry for disturbing you again.. but i have new idea about TDA7000, and i want you to tell your opinion ...
What if i want to use to only components after the IF stage, i.e. i will build my own Mixer and Oscillator followed by another IF amplifer, then connect its output to pin 12.. is this feasible now? .. please don't get upset from me and do reply again :)
Thanks alot in advance,
Ahmad,
You can do this, but there are probably other ICs specifically designed as IF strips-demodulators that would be easier to use.
That's great, can you suggest some of them to me?
These were common in the past. I do not know of any present model numbers.
You can make the amplifier chain yourself with PECL line receivers strung together. Then use a PLL chip for the demodulator.