| 摘要 |
<p>An RF transmitter suitable for ISM band transmissions has an IF modulator (120) and an RF modulator (150), the IF modulator being arranged to use a very-low-IF-frequency f IF , smaller than half the channel bandwidth, such that spurious unwanted modulation components fall in other channels having a channel number within one or two of a channel being transmitted. This can reduce the VCO pulling problem and reduce adjacent channel power degradation compared to using higher IF frequencies. The local oscillator PLL's fractionality is used in order to optimize the adjacent power frequency plan by selecting the most appropriate IF frequency. For the "Bluetooth ® Wireless Technology" application, the IF frequency is < 500kHz, and the main non-filtered spurious components (1LO.xBB with x:-3,-2,....,+3) image, carrier, pulling, for both 0 and 1 FM signals, are positoned in frequency bands of adjacent channels.</p> |
