Beware the hidden costs of working with RF ICs

Today's wireless SoCs offer the promise of reduced cost radio telemetry, but Barry Gillibrand warns that for most applications the hidden design costs can dominate.

The explosion of RF ICs onto the world market is mesmerising to say the least.

If Bluetooth or Zigbee or any of the other proprietary parts available is your "bag" then this article is not for you.

The following is aimed at those engineers working in the less "glam" wireless markets mainly concerned with ISM (industrial, scientific and medical) applications.

These cover a multitude of generally non-mass-market products for which nobody has yet written a general protocol.

In fact it could be argued that this would be positively a nuisance given the plethora of different products in this sector of the wireless industry.

So you want to make your next gismo wireless - doesn't everyone?.

What are the design options available and likely costs?.

Which option will get you to market ahead of the competition?.

The apparent "obvious" option, which appears to offer the lowest cost, is the massively promoted RF IC.

After all, the cost of the chip at around $3-5 looks like offering a very cheap radio.

Beware there are usually several external parts required and these can increase the cost considerably not to mention the necessary micro.

Don't fall into the trap of assuming that you can use the one you already have in your application to also run the radio - it will very rarely work as planned.

The marketing blurb from one of the early RF IC offerings made the bold statement that "your grandmother could design a radio with our chips".

Well assuming she had a PhD in RF engineering this was probably accurate.

And at $1.50 a crack it looked like a real cheap deal (RX only) - only three external components, how could you go wrong.

Our company set about making a "working" receiver based on this part and finally after several months of iterations came up with a half-decent AM RX; with a manufactured cost of about GBP 4.50/$9.00, a far cry from an easy design costing $1.50.

The addition of a SAW filter helped to push up the cost somewhat.

So these things are seldom what they seem at first glance.

To be fair to the RF IC guys they have improved their act significantly since the early days and now offer good quality radio chips with considerable help and support available as well as reference designs.

So is the radio design task so easy that you grandma can do it now - unfortunately not.

The apparent deluge of help available has lured many engineers into the belief that this is now straightforward and there is no doubt that very good radios can now be produced using many of the parts available - this is not the issue we are discussing here.

Given that your company has the manpower design resources, expensive RF test equipment etc, and most importantly plenty of that rare commodity - time - then a satisfactory radio can be achieved.

If your application is for considerable volumes because you operate in the consumer or automotive volume then you probably will need to go down the RF IC route.

However, if like thousands of companies you operate in more modest volume areas then a modular solution is going to be certainly quicker and - in the long run - more cost effective.

Our experience over the past 15 years suggests that the usual timescale to produce an approved radio, hardware only, using an RF IC is somewhere between 9 and 12 months.

Once the hardware w