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MICRF002 Datasheet(PDF) 8 Page - Micrel Semiconductor |
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MICRF002 Datasheet(HTML) 8 Page - Micrel Semiconductor |
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8 / 16 page  MICRF002/RF022 Micrel MICRF002/RF022 8 March 2003 In sweep-mode, a range reduction will occur in installations where there is a strong interferer in the swept RF band. This is because the process indiscriminately includes all signals within the sweep range. An MICRF002 may be used in place of a superregenerative receiver in most applications. Step 2: Selecting The Reference Oscillator All timing and tuning operations on the MICRF002 are de- rived from the internal Colpitts reference oscillator. Timing and tuning is controlled through the REFOSC pin in one of three ways: 1. Connect a ceramic resonator 2. Connect a crystal 3. Drive this pin with an external timing signal The specific reference frequency required is related to the system transmit frequency and to the operating mode of the receiver as set by the SWEN pin. Crystal or Ceramic Resonator Selection Do not use resonators with integral capacitors since capaci- tors are included in the IC, also care should be taken to ensure low ESR capacitors are selected. Application Hint 34 and Application Hint 35 provide additional information and recommended sources for crystals and resonators. If operating in fixed-mode, a crystal is recommended. In sweep-mode either a crystal or ceramic resonator may be used. When a crystal of ceramic resonator is used the minimum voltage is 300mV PP. If using an externally applied signal it should be AC-coupled and limited to the operating range of 0.1V PP to 1.5VPP. Selecting Reference Oscillator Frequency f T (Fixed Mode) As with any superheterodyne receiver, the mixing between the internal LO (local oscillator) frequency f LO and the incom- ing transmit frequency f TX ideally must equal the IF center frequency. Equation 1 may be used to compute the appropri- ate f LO for a given fTX: (1) f f 0.86 f 315 LO TX TX =± Frequencies f TX and fLO are in MHz. Note that two values of f LO exist for any given fTX, distinguished as “high-side mixing” and “low-side mixing.” High-side mixing results in an image frequency above the frequency of interest and low-side mixing results in a frequency below. After choosing one of the two acceptable values of f LO, use Equation 2 to compute the reference oscillator frequency f T: (2) f f 64.5 T LO = Frequency f T is in MHz. Connect a crystal of frequency fT to REFOSC on the MICRF002. Four-decimal-place accuracy on the frequency is generally adequate. The following table identifies f T for some common transmit frequencies when the MICRF002 is operated in fixed mode. t i m s n a r T y c n e u q e r F f X T r o t a l l i c s O e c n e r e f e R y c n e u q e r F f T z H M 5 1 3z H M 0 7 9 8 . 4 z H M 0 9 3z H M 0 3 6 0 . 6 z H M 8 1 4z H M 3 8 9 4 . 6 z H M 2 9 . 3 3 4z H M 8 5 4 7 . 6 Table 2. Fixed Mode Recommended Reference Oscillator Values For Typical Transmit Frequencies (high-side mixing) Selecting REFOSC Frequency f T (Sweep Mode) Selection of the reference oscillator frequency f T in sweep mode is much simpler than in fixed mode due to the LO sweeping process. Also, accuracy requirements of the fre- quency reference component are significantly relaxed. In sweep mode, f T is given by Equation 3: (3) f f 64.25 T LO = In SWEEP mode a reference oscillator with frequency accu- rate to two-decimal-places is generally adequate. A crystal may be used and may be necessary in some cases if the transmit frequency is particularly imprecise. t i m s n a r T y c n e u q e r F f X T r o t a l l i c s O e c n e r e f e R y c n e u q e r F f T z H M 5 1 3z H M 8 8 . 4 z H M 0 9 3z H M 5 0 . 6 z H M 8 1 4z H M 8 4 . 6 z H M 2 9 . 3 3 4z H M 3 7 . 6 Table 3. Recommended Reference Oscillator Values For Typical Transmit Frequencies (sweep-mode) |
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Similar Description - MICRF002 |
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