Silicon Labs single chip radios are amazing performers. A complete SDR smaller than your fingertip. And, they’re everywhere.
Silicon Labs is probably the world’s largest radio manufacturer – that you have never heard of! Twenty years ago, they built the world’s first CMOS frequency synthesizer for mobile phones. Over time, this Austin-based company has pioneered low-power mixed signal systems integration.
Until recently, their bread-and-butter business has focused on receiver-on-chip technology. They have shipped over a billion single chip TV tuners and radio receivers. Odds are that you already use them in your smart phone, media player, car entertainment system, table radio, portable radio or other consumer devices. Although the company focus has shifted heavily towards Internet of Things, radio tuners is still a big part of their business.
Silicon Labs single chip radios have a strong value proposition. By providing a nearly complete radio on a single chip, original equipment manufactures can reduce a typical radio bill of materials (BOM) by 90%. Basically, you can construct a full featured radio by just adding power, a few antennas, a microcontroller, and a few buttons and dials. Take a look at the complete current line of their radio chips. With these chips, no alignment is necessary.
Tuning can be digital or analog. Displays can be digital or analog. Coverage options include AM, FM, long wave, short wave or weather band. Just choose the appropriate chip. Some popular SWL portables from Tecsun and Grundig are based on these chips.
Silicon Labs Single Chip Radios – Digging In
Take a quick look at a data sheet, such as the Si4844-B shown above. Inside the device, you find a complete SDR, which uses QSD (quadrature sampling detection) down-converting to a Low IF. This approach reduces problems with images. Typically, these radios have image rejection > 70 dB, adjacent channel rejection of > 50 dB.With the Si4844, the local oscillator is either 45 kHz above or below the tuned frequency. Decent dynamic range, in the order of 75 dB, reduces the need for front end filtering.
Silicon Labs single radio chips are really smart. They run off firmware that is programmable using a small micro-controller over an I2C two-wire bus. Control of frequency, AFC and AGC are all configurable. Since many of the chips are found in automobiles, they have sophisticated noise blankers, as well. For AM reception, bandwidth is adjustable from 1 to 6 kHz. The chip measures signal strength (RSSI) and SNR and will make dynamic adjustments based on these. Some chips also decode RDI, and will shift to different frequencies based on quality of signal.
All pretty amazing. Unfortunately, stock firmware does not decode SSB/CW but it appears that some OEM create customized firmware that does.
Silicon Labs Single Chip Radios – Patents Galore
The company holds more than 1500 patents. If you are interested in the design of these chips, check out some of the patent filings. Three very interesting patents are:
- Integrated Low-IF Terrestrial Audio Broadcast Receiver and Associated Method (2004)
- Unconditionally Stable Analog-to-Digital Converter (2006)
- Dynamic Selection of Local Oscillator Signal Injection for Image Rejection in Integrated Receivers (2006)
You can read these through Google Patents. They provide an amazing amount of design information, and make up for the lack of detail in the company data sheets.