전자부품 데이터시트 검색엔진 |
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AD6423 데이터시트(PDF) 3 Page - Analog Devices |
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AD6423 데이터시트(HTML) 3 Page - Analog Devices |
3 / 8 page AD20msp415 –3– REV. 0 AUXILIARY SYSTEM FUNCTIONS The GSMP and the VBC perform a number of auxiliary func- tions that are essential to build a complete mobile radio. A general radio section constitutes the three functions of trans- mitter, receiver and synthesizer. Figure 2 shows how the baseband chipset interfaces to a typical radio architecture. The transmitter is fed with baseband analog I and Q signals from the VBC and upconverted to 900 MHz for GSM applications and 1800 MHz for PCN applications. A dedicated power amplifier increases the RF signal to the required level. The receiver amplifies the antenna signal, down- converts it to an intermediate frequency (IF) and amplifies it there again. After second conversion to baseband the I and Q components of the signal are fed into the VBC. The three auxiliary functions, AGC, AFC and Power Ramping are included to interface to the radio section. Power Ramp Envelope To meet the spectral and time-domain specifications of the transmitted output signal, the burst has to follow a specified power envelope. The envelope for the power profile originates in the GSMP as a set of coefficients, down-loaded and stored in the VBC. This envelope profile is fed to the RAMP DAC on the VBC with each burst. The analog output is fed into the RF power amplifier, controlling the power profile and absolute level of the transmitted data. The power control loop of the power amplifier can also feedback an error control signal that indicates whether the output functions are out of specification and the radio can be switched off accordingly. Automatic Gain Control (AGC) The mobile radio has to cope with a wide range of input signal levels. The major part of the overall gain is provided in the IF amplifier. The incoming signal level is analyzed in the GSMP and a digital gain control signal is sent to the VBC. The AGC DAC generates the appropriate analog control signal for the IF amplifier. Automatic Frequency Control (AFC) The mobile radio tracks the master clock provided by the base station to compensate for temperature/frequency drifts in the crystal oscillator. Drift of the crystal oscillator over time and temperature has to be compensated as well as frequency shifts due to the Doppler effect in the case of a moving mobile radio. The received signal is analyzed in the GSMP and a digital con- trol signal is generated. This signal is sent to the AFC DAC in the VBC to control the voltage controlled, temperature compen- sated crystal oscillator (VCTCXO). Synthesizer Control The GSMP and the respective parts of the Layer 1 software control the overall timing and frequency generation of the radio subsystem. This includes control signals for two synthesizers, power-down control signals and power amplifier monitor sig- nals. Detailed information can be found in the AD6422 data sheet. SYNTHESIZERS RADIO SUBSYSTEM CONTROL AGC AFC CLOCK PAERROR AGC DAC I Q Q GSMP BASEBAND/AUXILIARY SECTION OF VBC DIGITAL FIR FILTER GSMSK MODULATOR BURST STORE PA IF Tx DAC Tx DAC RAMP DAC AFC DAC SUB DAC DIGITAL FIR FILTER DIGITAL FIR FILTER DIGITAL FIR FILTER DIGITAL FIR FILTER SERIAL BASEBAND PORT SERIAL AUXILIARY PORT RAMP RAM RAMP CONTROL Rx ADC Rx ADC 13MHz VCTCXO Figure 2. Control of Radio Subsystem |
유사한 부품 번호 - AD6423 |
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유사한 설명 - AD6423 |
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