AN1997| Application Note
Maxim/Dallas > App Notes > WIRELESS, RF, AND CABLE Keywords: rf, phs, transceiver, wireless, rfic, spectrum
Apr 28, 2003
APPLICATION NOTE 1997
500mW PHS Transmitter Meets Transient Spectrum Requirements with Edge Control
If the control signal's transition time is not controlled, the output spectrum of a 500mW PHS base station cannot meet the requirement. To use the MAX2510, only a simple circuit is added to insure a clean output spectrum during On/Off transients.
Introduction
The MAX2510 is a highly integrated IF transceiver for digital wireless applications. This is a ideal part to be used in PHS basestation application. Currently, the MAX2510 has been designed-in to a 20mW and 200mW PHS Base Station in China. However, when the MAX2510 is used in a 500mW output power PHS Base Station application, system characterization found that the spectrum re-growth does not meet the specification for spectral quality. This failure to meet spectral requirements was found to be due to high power output and a steep rising edge of the transmit-gate control signal. This document presents the design trade-offs and simulation to reduce the spectral re-growth by adding slope control on the transmit-gate signal.
Design Target
The 500mW PHS basestation specification requires that the spurious emissions are 800nW, 250nW, 2.5mW at an offset from the center frequency of 600 kHz, 900 kHz and out-of-band respectively. The spurious energy is measured in a 30 kHz bandwidth. There are three types of PHS basestation output-power ratings: 20mW, 200mW, and 500mW. These output power levels are measured in a bandwidth of 300 kHz. The table below lists the requirements for different output power PHS basestations. Table 1 Output Power -> Spurious Emission 800nW 250nW 2.5uW
Offset Frequency 600kHz Offset 900kHz Offset Out of band
20mW 34dBc 39dBc 29dBc
200mW 44dBc 49dBc 39dBc
500mW 48dBc 53dBc 43dBc
Design Approach and Simulation
In order to meet the above spectral re-growth requirement, we need to carefully design an analog slope-control circuit for the TX gate signal. The output power is controlled by a logic-level signal and the power ramp-up and ramp-down duration is limited to within 13us.
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