Author: Richard Abrahams This Application Note describes circuitr

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Elimination Transient Start-Up Logic State PRISM® 2.4GHz Direct Sequence Reference Radio
Author: Richard Abrahams
This Application Note describes circuitry eliminate transient start-up logic state AM79C930 PCnetTMMobile Media Access Controller used Intersil PRISM® Direct Sequence Wireless Radio reference Design. start-up transient logic state cause burst undesired transmission and/or possible damage HFA3925 Power Amplifier. When power first applied circuit, AM79C930 MAC, asserts PA_PE line (U3, 131) high approximately 125ms before going state. During this time, transmit in-band spurious signals that emanate from uncontrolled radio. Furthermore, negative bias voltage generated DC-DC Converter (ICL7660), takes approximately build Operating HFA3925 without proper negative bias recommended circuit will draw high supply current approximately 850mA. This PA_PE state only occurs initial power-up does affect operation radio during "sleep" mode power management modes.
applied, begins charging through baseemitter voltage above threshold (approximately 0.6V) saturated Base drive therefore shunted ground PA_PE drive inhibited. charges, current exponentially decays towards zero. Eventually point reached where base-emitter voltage sustain conduction. turns PA_PE drive enabled.
Cards
card design, since power drain less critical, switching done level. switching circuitry therefore been simplified compared PCMCIA design that level translating switching transistor, Figure been eliminated. result this change, inverter used generate PA_PE directly control supply switch (Figure PA_PE active low, required transient suppression circuit dual that used PCMCIA card. With reference Figure below, 1.5K resistor, been added series with PA_PE line gate switching FET, This resistor provides convenient access point disabling PA_PE drive under start-up conditions. remainder transient suppressing circuit functions identically that used PCMCIA card with exception that circuit been flipped over dual version utilizing MMBT2907 transistor inhibit PA_PE drive gate While capacitor charging, transistor conducts shunts gate drive source thereby turning device removing switched from
circuits shown below inhibit PA_PE drive approximately 200ms after power turn-on. PCMCIA cards require different circuitry switching variations PA_PE signal path.
PCMCIA Cards
With reference Figure below, additional circuitry consists resistors, capacitor transistor. Initially, fully discharged. When power
VCC_PA EXISTING CIRCUIT PA_PE 4.7µF 470K SWITCHED
VCC_PA
470K 4.7µF PA_PE 1.5K
MMBT2222
MMBT2907
IRLM6302 EXISTING CIRCUIT
SWITCHED
FIGURE CIRCUIT PCMCIA CARD
FIGURE CIRCUIT CARD
Intersil semiconductor products manufactured, assembled tested under ISO9000 quality systems certification.
Intersil semiconductor products sold description only. Intersil Corporation reserves right make changes circuit design and/or specifications time without notice. Accordingly, reader cautioned verify that data sheets current before placing orders. Information furnished Intersil believed accurate reliable. However, responsibility assumed Intersil subsidiaries use; infringements patents other rights third parties which result from use. license granted implication otherwise under patent patent rights Intersil subsidiaries.
information regarding Intersil Corporation products, site http://www.intersil.com
4-259
http://www.intersil.com 407-727-9207 Copyright Intersil Corporation 1999 PRISM PRISM logo trademarks Intersil Corporation. PCnetis trademark Advanced Micro Devices, Inc.

Author: Richard Abrahams This Application Note describes circuitr

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