Power supplies are part and parcel of electronic circuits and are needed in a variety of forms to drive these circuits. Some familiar terms include dc-dc converters, battery chargers, voltage regulators, and voltage references. Normally, these supplies are external to the semiconductor chips, modules or circuit boards they are driving. In fact, with growing complexities of circuits, each chip, module or board requires several different voltages to operate. Thus, seeing multiple dc-dc converters and voltage regulators on a single circuit board is not uncommon.

However, advances in process technologies coupled with the drive to pack more on a single chip, some RF suppliers have taken the first step in integrating a power management unit (PMU) on the same RF die or bringing it inside the same semiconductor package. A good example is the recent introduction of Silicon Laboratories SiRX RF front-end chip for direct broadcast satellite (DBS) applications. With tuner, demodulator and low-noise block (LNB) converter supply functions integrated on the same CMOS RF die, it substantially cuts design time and lowers BOM cost. The built-in LNB supply controller with a typical switching frequency of 264 kHz provides a step-up dc-dc on-chip, and offers up to 18 V with about 80% efficiency and current rating of 500 mA to 750 mA, as well as provides short-circuit and overcurrent protection.

This is not the only RF chip from Silicon Laboratories that boasts PMU on the same die along with other RF functions. Recently, the company also unveiled a 0.13-micron CMOS-based integrated single-chip solution for the cost-sensitive GSM/GPRS handsets. This fully functional single-chip phone integrates on-chip a PMU, battery interface and charging circuitry, along with digital baseband, analog baseband and a quad-band RF transceiver. The battery charging circuit is programmable for a variety of chemistries. Plus, it integrates low dropout (LDO) regulators for internal and external subsystems.

Other RFIC players to signal this trend include Analog Devices Inc. (ADI) and RF Micro Devices (RFMD). Both key RFIC players see the need to bring power management functions on board. ADI's quad-band Othello-E transceiver combines all the radio and power management functions for an ultracompact, cost-effective EDGE radio on a single 0.35 micron BiCMOS chip. On-chip three LDO voltage regulators enable direct connection to the battery supply, eliminating the external regulators and reducing BOM component count and cost.

Likewise, RFMD is also moving aggressively on this front as it recognizes that managing power within a cell phone is becoming extremely critical. Although the company has readied a stand-alone buck dc-dc converter with more than 90% conversion efficiency to power CDMA/WCDMA power amplifiers (PAs), it is developing shielding, isolation and circuit techniques to bring such power supplies, including external passives, inside the PA multichip module. The technologies under development will mitigate noise, interference and crosstalk in such integrated RF solutions. The plan is to achieve these goals within a year. By the way, this stand-alone buck converter incorporates a current-mode PWM controller with integrated power MOSFETs and switching frequency of more than 2 MHz. Incidentally, for lower-power Bluetooth applications, RFMD designers have accomplished that goal. The company intends to sample pretty soon an integrated RF Bluetooth chip with onboard switch-mode dc-dc converter. Going forward, the company is also eyeing higher-power GSM standards. Leveraging its knowledge of designing single-phase converters for WCDMA handsets, it is now developing a stand-alone two-phase power solution for GSM applications with the objective to integrate such multi-MHz switch-mode supplies inside the same GSM PA module with the ultimate goal of integrating the power management circuits with RF functions on the same die.

In essence, as the process technologies advance and on-chip RF integration density increases, power management is becoming crucial. And the drive to integrate dc-dc converters, voltage regulators and other power sources becomes important to attain time to market, performance and cost objectives.

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