Electronic Design

ICs Keep AM/FM Radio On Top Of Broadcast Media

Who would've thought that the oldest technology in electronics, analog radio, would still be a big success today? Yet AM and FM continue to thrive despite digital HD radio's availability throughout the U.S. Now, Silicon Labs' latest radio chips support and even enhance AM/FM's viability.

The Si4730 and Si4731 support the worldwide AM and FM bands, 520 to 1720 kHz and 76 to 108 MHz, respectively. These single-chip radios only need an external AM antenna coil and capacitor, a clock crystal or signal, and a power bypass capacitor to work.

The FM antenna can be a 6-cm copper loop on the pc board. An external embedded controller controls the radio. The chips need external power amplifiers to drive the speakers or headphones.

With their 3- by 3-mm quad flat no-lead (QFN) package and few external components, the Si4730 and Si4731 are the smallest AM radios on the planet. They can fit into almost any portable device, like cell phones and MP3 players. Also, they can shrink standard products like clock radios and stereos.

The Si4731 includes the increasingly popular European Radio Data System (RDS) and U.S. Radio Broadcast Data System (RBDS). These standards transmit the station's call letters and frequency as well as music titles and artist names for display.

Basic AM/FM radios have suffered from a lack of both sensitivity and selectivity. The Si4730 and Si4731 should bring performance back with their high gain and sophisticated DSP filtering. They use IQ mixers and a low IF of 128 kHz (see the figure). They also feature seek, digital tuning, automatic gain control (AGC), automatic frequency control (AFC), programmable de-emphasis, and adaptive noise suppression. No external tuning or adjustments are required.

Meanwhile, Silicon Labs' Si4720 and Si4721 analog FM transceivers contain a standard FM radio with features and performance similar to the Si4730 as well as an FM transmitter that can be used to send MP3 music to any car radio for play through the sound system. Transmitter inputs may be digital directly from the MP3 player or analog signals.

The Si4721 includes the RDS/RBDS feature. Most other FM transceivers require as many as 57 external components, but the Si4720 and Si4721 only need a capacitor and 120-µH inductor at the antenna. As in the Si4730 and Si4731, the FM antenna can be a short pc-board copper loop. The package is a 3- by 3-mm QFN, making these transceivers small enough to incorporate in almost any product.

The Si4730 and Si4731 cost $4.87 and $5.53, while the Si4720 and Si4721 cost $5.26 and $6.31, all in 10,000-unit volumes.

Silicon Laboratories Inc.

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