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Maxim > Design Support > Technical Documents > Application Notes > Wireless and RF > APP 5281
Keywords: ISM, RF, radio frequency, impedance matching, transmitter, remote keyless entry, RKE,
wireless remote, ASK, FSK, drain efficiency, battery life, high transmit power, 433.92MHz, European
frequency, ETSI
APPLICATION NOTE 5281
Flexible Configuration of the MAX7060 ASK/FSK
ISM-RF Transmitter
By: Richard Young
Apr 03, 2012
Abstract: This application note illustrates the flexibility of the MAX7060 ASK/FSK transmitter. While the
currently available evaluation kit (EV kit) has been optimized for the device's use in a specific frequency
band (i.e., 288MHz to 390MHz), this document addresses how the EV kit circuitry can be modified for
improved operation at 433.92MHz, a frequency commonly used in Europe. Two alternative match and
filter configurations are presented: one for optimizing drain efficiency, the other for achieving higher
transmit power. Features and capabilities of earlier Maxim industrial, scientific, and medical radio-
frequency (ISM-RF) transmitters are provided, allowing comparison of the MAX7060 to its predecessors.
Several design guidelines and cautions for using the MAX7060 are discussed.
Introduction
The MAX7060 ASK/FSK transmitter is an IC that is all about
flexibility. First of all, it is flexible in frequency, with a fractional-N
PLL capable of operating either from 285MHz to 420MHz (with a
15MHz crystal), or from 304MHz to 448MHz (with a 16MHz
crystal), in steps as fine as f
XTAL
/4096. This allows transmission at
all major industrial, scientific, and medical system (ISM) frequencies
below 450MHz, including ones that might only be available in
certain geographic areas. The fractional-N architecture also allows
for extremely accurate FSK modulation, allowing data rates of up to 70kbps Manchester-coded.
The MAX7060 is also flexible in transmit power, designed with an integrated voltage digital-to-analog
converter (VDAC) to provide an exponentially scaled voltage to the power amplifier (PA). When the IC is
operated with a sufficient V
DD
, the VDAC enables nearly 30dB of adjustment range in approximate 1dB
steps. This power-stepping capability can also be used for envelope shaping when transmitting ASK,
thereby facilitating conformance to regulatory requirements in both the U.S. and overseas markets.
Flexible PA matching is available by means of a programmable capacitor, which is selectable from 0 to
7.5pF in increments of 0.25pF. During system testing, the transmitter performance at a given operating
point (transmit frequency and PA code) can be optimized by finding the "cap code" (i.e., capacitance
code) that minimizes current drain and/or maximizes efficiency for that set of conditions. It also permits
the PA load to be tuned as necessary to adapt to changes in the operating environment.
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