Power amp boosts wireless LAN range

A new RF power amplifier with integrated detector from Intersil is designed to boost the performance of wireless LAN systems.

A new RF power amplifier with integrated detector from Intersil is designed to boost the performance of wireless LAN systems.

The ISL398's higher output power increases wireless range by up to 15% and doubles the data throughput at maximum range.

It also automatically monitors and controls power consumption using an integrated detector with "sleep mode" function to extend battery life.

Intersil's new PA is designed to work with the complete range of PRISM wireless local area networking chipset solutions operating in the 2.4GHz band.

It is ideal for current Wi-Fi 802.11b and emerging higher speed 802.11g applications including wireless access points.

In a typical application such as PRISM WLAN system, the HFA3861B or HFA3863 baseband processor uses the detector's output to dynamically control the ISL3985's output power.

The output power is optimised as needed by automatically adjusting the automatic gain control voltage of the HFA3783 IF quadrature modem.

This provides the best possible error-free data transfer rate in a given operating wireless environment and helps compensate for channel-to-channel and temperature related variability in the transmit chain while reducing power consumption.

Applications for the ISL3985 include: access points and WLAN cards for IEEE802.11b and g applications; other 2.4GHz industrial scientific and medical (ISM) band radios; and 2.4GHz time division multiplex access (TDMA) packet protocol radios.

The ISL3985 is a 2.4GHz two-stage radio-frequency power amplifier (RFPA) with a built-in detector.

Cascaded output power is typically 21dBm for the usual direct sequence spread spectrum (DSSS) signal and exceeds adjacent channel power ratio (ACPR) specifications with less than -30dBc for the first side lobe and less than -50dBc for the second side lobe.

The integrated detector is accurate within +/-1dB over a 15dB range.

This allows an accurate automatic level control function to be implemented.

The ISL3985 is packaged in a very small 16-pad, 5 x 5mm quad flatpack no leads (QFN) package that conserves space and provides highly effective heat sinking to the main board.

The ISL3985's power detect function provides a DC output voltage proportional to the logarithm of the output power.

The detector is accurate to within 0.5dB at an output power of 21dBm.

The slope of the detector output voltage is 100mV/dB over a 15dB dynamic range.

A simple use for the detector is to optimise output power compensating for manufacturing deviations.

The ISL3985's "sleep mode" (power up/down) function is fully integrating on the chip and does not require any external circuitry.

This frees up board space and reduces component count and cost.

When the CMOS-compatible power enable (PE) pin is driven low, the total supply current to the RFPA drops to less than 50uA, typically in as little as 300ns.

Full output power returns within a few hundred nanoseconds when the PE pin is driven high.

The ISL3985 extended range power amplifier is available in production volumes now.

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