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Original Publication Date: 1997-Dec-01
Included in the Prior Art Database: 2002-Jun-12

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Randall Hillock


In a time division duplex (TDD) system the radio transmits and receives on the same frequency. The transmission and reception are offset in time. Often the transmission slot and the reception slot are adjacent in time and only a small guard time separates them. In many applications this time is rless than 4 p. sec. To accommodate this require- ment a transceiver must be able to switch between eception and transmission and visa versa very quickly. A typical transceiver for the ISM band that satisfies this requirement is shown below in Figure 1, Fig. 1 The diagram in Figure 1 is a wireless data trans- ceiver intended the ISM band. Dual-conversion in the receiver is used in order to achieve 50 dB of selectivity at 4 MHz offset (I MHz channels). The signal used for transmission is generated by dividing the 650 MHz offset PLL by two and then mixing this 325 MHz signal with the 2075-2175 MHz PLL signal to form a 2400-2500 MHz signal. Reception is accomplished by mixing down the 2400-2500 MHz input signal with the 2075-2175 MHz PLL signal to form a 325 MHz first IF signal. Then, the 325 MHz IF signal is mixed down with the 314.3 MHz PLL to form a 10.7 MHz second IF signal. This 10.7 MHz signal is fed into a detector.