Circuit arrangement for a phase locked loop

摘要

For rapid switching between alternative frequencies, the oscillator frequency (fOUT) is produced by a main loop (3) comprising a phase detector (30), a loop filter (32), a charge pump (31), a VCO (33), a fixed frequency divider (34) and a change-over switch (35) to which defined frequencies (fA1, fA2) are supplied from the auxiliary loops (1, 2). A reference circuit (5) contg. a crystal oscillator (51) and variable frequency divider (52) furnishes the reference frequency (fR) for the auxiliary phase detectors (10, 20). The corresp. lock detectors (176, 27) supply digital outputs (LD1, LD2) to an evaluation circuit (4) which operates the change-over switch.