AN903| Application Note
Maxim/Dallas > App Notes > WIRELESS, RF, AND CABLE Keywords: WLAN, FHSS, LNA, VCO, PA, 802.11b, power amplifiers, voltage controlled oscillators, system diagram
Jun 01, 2001
APPLICATION NOTE 903
RF ICs for 2.4GHz ISM-Band FHSS Solutions: Bluetooth, HomeRF, DECT Applications
WLANs and related systems are compared. IEEE802.11b FHSS supports 1.6Mbps data transmission. MAX2644 SiGe LNA serves as the PA driver and the receiver low noise amplifier (LNA) in the 2.5GHz band. The MAX2240 and MAX2242 power amplifiers (PA) produced the ~+20dBm output with the needed linearity. The MAX2754 VCO offers highly linear modulation and on-chip varactors. Additional Information:
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Wireless Product Line Page Quick View Data Sheet for the MAX2240 Quick View Data Sheet for the MAX2242 Quick View Data Sheet for the MAX2244 Quick View Data Sheet for the MAX2644 Quick View Data Sheet for the MAX2754 Applications Technical Support
Overview
In the unlicensed 2.4GHz ISM band, the FCC dictates the use of either frequency-hopping spread spectrum (FHSS) or direct-sequence spread spectrum (DSSS) technology. FHSS systems are targeted at low-cost lowpower low-range low-data-rate applications, and include Bluetooth, HomeRF (SWAP), 2.4GHz DECT (digital European cordless telephone), and FHSS IEEE802.11. The DSSS IEEE802.11b systems are intended for higherdata-rate and higher-range applications, and typically cost more and consume more power. Bluetooth systems are directed at data transfer, such as transferring an e-mail message from a cell phone to a PDA, and support data rates up to 721kbps. HomeRF supports both data and voice transmission, and allows data rates up to 1.6Mbps. Carrying over from its past incarnation at 1.9GHz, 2.4GHz DECT is intended for 2.4GHz cordless phones with a data rate of 552kbps. IEEE802.11 FHSS systems currently support data rates up to 1.6Mbps, but a new 5-MHz channel bandwidth allocation, wideband FH, will allow symbol rates
up to 10Mbps. This will let FHSS compete with the current 11Mbps symbol rates supported by DSSS systems. For FHSS, the 2.40GHz to 2.835GHz ISM band is broken into 75 1MHz channels, with a 2MHz lower guard band and a 3.5MHz upper guard band. All FHSS systems are based on TDMA, with the number of frequency hops per second varying from one standard to another. Bluetooth and DECT utilize Gaussian frequency-shift keying (GFSK) modulation, whereas HomeRF and FHSS 802.11 use 2-level and 4-level frequency-shift keying (FSK), to take advantage of the higher efficiencies offered from saturated power amplifiers (PAs). The following block diagram shows a typical application.
RF Receiver ICs
There are many single RF IC transceiver solutions for FHSS radios; however, quite a few of these solutions lack a low-noise amplifier (LNA), a PA, a PA predriver, or a voltage-controlled oscillator (VCO). On the receiver side of the radio, Maxim offers the MAX2644 LNA, with 17dB of gain and a 2.0dB noise figure at 2.45GHz. Adding the
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