AFC CIRCUIT AND METHOD FOR DUAL-MODE MOBILE TELEPHONE WITH ACQUSITION STATES

摘要

An AFC (Automatic Frequency Control) device and a method of controlling reception frequency in a dual-mode terminal. When a dual-mode terminal uses one or two AFC devices, the time required for acquiring tracking synchronization in a PLL circuit for a first frequency can be reduced using a test augmentation frequency which is an integer multiple of a tracking synchronization acquiring residual frequency of a PLL circuit for a second frequency to which the first frequency transitions for reliable synchronization acquisition. Errors with respect to an output dynamic range caused by use of two AFCs are reduced and thus the demodulation performance of a receiver is ensured by varying quantization bits of an A/D clock based on the dynamic range of residual errors in a frequency area. The demodulation performance can also be ensured by operating an ACPE circuit for an AFC device having many residual frequency errors. In this method, the frequency characteristics of the dual-mode terminal are stabilized and the stability of a demodulator is increased due to a frequency offset. As a result, stable demodulator performance is ensured.