The MAX2395 is a fully monolithic quasi-direct conversion modulator IC made for use in WCDMA/UMTS transmitters. Due to its internal architecture, the RF output frequency is at 5/6 of the RF LO frequency, which is generated from an on-chip integer-N PLL. Since the raster frequency in a WCDMA system is 200kHz, the MAX2395 PLL needs to provide a 240kHz step size (ie 6/5 times 200). For the most popular reference frequencies in WCDMA user-terminal applications, such as 19.2MHz and 15.36MHz, the 240kHz comparison frequency can be easily generated by the internal PLL integer divider, 80 and 64 respectively. The Maxim evaluation board was designed with a 19.2MHz reference in mind. In a UMTS system, a 13.0MHz or 26.0MHz reference frequency is often used, which is not an integer multiple of 240kHz. So the comparison frequency used by the MAX2395's PLL needs to be reduced to a number whose multiple is 240kHz and 13.0/26.0MHz. For the 26.0MHz crystal, the comparison frequency commonly used is 80kHz, which permits a 240kHz channel raster by using three 80 kHz steps. The 80kHz PLL frequency represents 3 times greater "divide-by-N" value for the same LO, which results in 10dB increased close-in phase noise (20 log N). The EVM (error vector magnitude) will be also degraded, since the PLL contribution to EVM is roughly proportional to its integrated phase error. The comparison spurs get lower attenuation from the loop filter, so the loop filter needs to be re-designed to balance integrated phase error, settling time and comparison spurs attenuation.