Low-end cell leans on analog

Designed primarily for the entry-level cell phone user and first launched in Brazil, Kyocera's K112 handset nevertheless supports a fairly rich feature set, including games, calculator, ring tones and an alarm-one of my favorite little extras. On a more technical note, the handset also features an internal antenna-an amazing bit of RF engineering in itself-to bypass all those breakage-prone stubs and whips.

The single-band CDMA/AMPS K112 is based on Qualcomm Inc.'s recent cdma2000 standard-designed to improve communications efficiency over that of the original IS-95 CDMA protocol. More important from an electronics viewpoint, the design was one of the first handsets we analyzed that uses Qualcomm's radioOne chip set with a zero-intermediate-frequency architecture, also known as direct conversion.

Keep in mind that the "digital cell phone" still relies on an analog carrier of bit streams-whether for voice or data-so radio complexity remains significant. The CDMA direct-conversion architecture results in fewer components than the previous, multistage up-/downconversion radios, but it lags behind the simplifications seen in GSM designs.

The digital baseband processor in the Kyocera model (MSM6000) is paired with two main radio devices, one for the transmit path (RFT6102) and one for the receive path (RFR6002). Separation of the transmit and receive devices reflects some distinctly analog issues in managing interference and keeping clean communications pathways, given the simultaneous transmit and receive activity inherent to code-division multiple access.

Incoming signals are piped through a duplex filter to a low-noise-amplifier (RFL6000) to boost signal levels. Meanwhile, oscillators from Kyocera generate the appropriate radio frequencies for mixing inside the radio chips. A gallium arsenide power amplifier module from RF Micro Devices (RF6000-2) is tasked with boosting output signals to the device's internal antenna.

Power management at the system level comes via a dedicated analog ASIC (PM6000) responsible for generating the multiple chip supply voltages and handset lighting required. Because supply functions have been rolled up in the PM6000, there is a notable absence of small-scale regulators on the board. Only a charge controller chip and a smattering of transistors are required to complete the power-management chain.

Despite the relatively inexpensive CDMA handset cost structure for the K112, low cost cannot come at the expense of dropped signals and poor battery life. As such, the analog content in this entry-level phone actually contributes to the system cost structure at a level similar to that of the digital baseband. Of course, the analog goodies also contribute to the most important thing of all: making the call.

David Carey, president of Portelligent. The Austin, Texas, company produces teardown reports and related industry research on wireless, mobile and personal electronics (www.teardown.com).

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