Misuse of a TA7642 (MK484)

[richard.cs]

The well known AM TRF receiver on a 3-pin chip. Datasheet: http://www.shenzhensum.com/products/datasheet/TA7642.pdf

While the last stage is nominally a detector it looks (from the equivalent circuit and from the fact that people have made regenerative sets from them) like if the 100n is left off of the output and perhaps the bias is tweaked a little then most of the amplified RF still comes out. If so that would make it rather useful for something I'm working on which needs a fairly wideband input stage centred on 1 MHz. I'm going to order a few and have a play but in the meantime a few questions:

Is there a similar part without the detector (or with the intermediate connection brought out)?
Has anyone here used one for this purpose?
Does anyone have any spice models for the part?
Failing that some suggestions for transistor parameters to try in a model of the equivalent circuit would be appreciated.


Thanks
Richard

[dannyf]

I have used it as an if amplifier 455khz. No problem. And with the added advantage of built in agc.

selectivity however isn't that great.

[SeanB]

What about using one of the MAR series microwave amplifiers? Yes incredible overkill, and you will need to take care not to make an oscillator out of it but they actually do have a good gain figure down to audio frequencies. Plus as a bonus you have 50R input and output impedances.

[dannyf]

Those MMICs have very low input impedance, making them unsuitable for tuned RF circuits, unless you do impedance matching.

[richard.cs]

Danny - you used it purely as an IF amplifier without making use of the detector? i.e. 455 kHz in and out. This is the kind of thing I have in mind.

Sean - I've looked at the microwave amplifiers. The low input imedance is probably ok in my application and I think they should work with care but several stages would be needed for similar gain. This may be what I end up with, I'll already be using that type of thing elsewhere in the design for stuff at around 100 MHz.

[dannyf]

No. In my case, it was if plus the detector.

I haven't attempted to drive an if can with it but don't see why it cannot be done - the bias in the last stage isn't too low.