The Si4831/35-B30 is the 2nd generation mechanical-tuned digital CMOS AM/FM/SW radio receiver IC that integrates the complete receiver function from antenna input to audio output. Like other successful audio products from Silicon Labs, Si4831/35-B30 offers unmatched integration and PCB space savings with minimum external components and a small board area.
It is some time passed by since I wanted to try one of those Silicon Labs DSP-type radio receivers chips.
Looking through the Silicon Labs website I found that they also have some devices which do not need an external processor for using them, instead one can use a simple variable resistor. This looked very easy and interesting, the only problem was to found some of those devices.
After getting some of this tiny ICs the experiment could start. Since the ICs come in a SSOP package I used an adapter board compatible with the normal raster of the usual PCBs for general purposes. Having this done there is not so much left to do, one just need a couple of devices to complete the radio. I mainly followed the schematic found in the data sheets and application notes, although I skipped the pre-amplifier stated to be required for shortwave (I did not had such a transistor at hand, and using what I had just made things worse). The only problem I experienced was a misinterpretation - the datasheets state that the crystal between pins 18 and 19 is optional. However I found that this device can not be left out and that the term 'optional' is somehwat irritating. So here is how the schematic looks like:
Looks pretty simple, right? On the AF side I used a TDA7052A which should later be replaced by a TDA2822 as soon as I get it. The Si4835 is powered by a 2.5V regulator (the device must not be powered by more than 3.6V). Testing the little radio I found that in the shortwave bands the reception was somewhat unstable, so I added an extra 100n cap across the tuning variable resistor which eliminated this problem completely. So here are two images of the somewhat 'finished' (and not very professional looking) radio:
So what about the performance? To give a short summary - I am impressed. Sensitivity is good (maybe not comparable with a good world receiver, but hey - just compare the price and effort...), I also like the quality of the audio signal on AM and the SW bands. The noise on SW and AM is rather low and fading effects are compensated in a wide range.
In all I am pretty satisfied with this device. Next I will look for smaller potentiometers and switches to minimize the needed size and maybe combine it with my already tested solar charger for the batteries to make a small but powerfull travel radio. Let's see...
Si4831/35 Mechanically-Tuned AM/FM Radio Receiver IC