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ML2721DH Datenblatt(PDF) 10 Page - Micro Linear Corporation |
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ML2721DH Datenblatt(HTML) 10 Page - Micro Linear Corporation |
10 / 27 page ML2721 10 January, 2000 PRELIMINARY DATASHEET PRELIMINARY I.F. FILTER LIMITING AMPLIFIERS ILO RECEIVER RX INPUT QLO RSSI AGC F V DATA FILTER DOUT RSSI ∫ Figure 1. Receiver Block Diagram MODES OF OPERATION OVERVIEW n STANDBY: All circuits powered down, except the control interface (Static CMOS) n RXCAL: Receive Calibration. PLL lock up time and IF filter alignment, prior to RECEIVE n RECEIVE: Receiver circuits active n TXCAL: Transmit Calibration. PLL lock up time prior to TRANSMIT n TRANSMIT: PLL open loop, modulated RF output available from IC The four operational modes are RXCAL, RECEIVE, TXCAL and TRANSMIT. They are set by the RXON (pin 2) and PLLEN (pin 3) control pins. XCEN (pin 1) is the chip enable/disable pin and can be set for standby operation. The relationship between the parallel control lines and the mode of operation of the IC is given in Table 2. PARALLEL MODE CONTROL The ML2721 is intended for use in TDD and TDMA radios in battery powered equipment. To minimize power consumption it is designed to switch rapidly from a low power mode (STANDBY) to receive or transmit. The ML2721 can also make a quick transition from receive to transmit for TDD operation. Prior to transmitting or receiving time should be allowed for the PLL to lock up, and in the case of receive, for the IF filters to be aligned. The ML2721 operates as a TDD radio on one RF frequency (transmit or receive). The VCO frequency changes between receive and transmit functions because of the IF frequency. This VCO frequency step is automatically performed. Table 2. Mode Selection RECEIVE MODES RXCAL AND RECEIVE In RECEIVE mode, the received signal at 900MHz is down converted, bandpass filtered (IF filter), fed to the frequency-to-voltage converter and low-pass filtered. The output of the low-pass filter is fed to the data slicer which outputs NRZ digital data. An RSSI voltage output indicates the signal level at the output of the IF filter. Prior to receive mode the ML2721 should be switched to RXCAL mode. This is to allow the IF filters to be aligned and for the PLL to switch frequency and settle to the required frequency for receiving. Filter alignment, using the Reference Frequency input signal REF, in the RXCAL mode sets: n Discriminator center frequency n IF filter center frequency and bandwidth n Receiver data low pass filter bandwidth n Transmit data low pass filter bandwidth In receive mode the programmed center frequency sets the RF channel that will be received. This means the PLL center frequency is the programmed RF center frequency plus the IF frequency. The frequency offset required for the low frequency IF in the RXCAL mode is automatically calculated and performed. RECEIVER CIRCUIT OPERATION The ML2721 receive chain is a low IF receiver using advanced integrated radio techniques to eliminate external IF filters and minimize external RF filter requirements. No external support circuitry is required other than supply decoupling and input matching. The precise filtering and demodulation circuits give improved performance over conventional radio designs using external filters. See Figure 1. N E C XN O X RN E L L Pe d o M 0X X Y B D N A T S 111 L A C X R 11 0 E V I E C E R 10 1 L A C X T 10 0 T I M S N A R T |
Ähnliche Teilenummer - ML2721DH |
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Ähnliche Beschreibung - ML2721DH |
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