A read clock circuit selectively provides a read clock signal from a memory to a memory controller over a memory bus. A pulse-amplitude modulation (PAM) driver including an input and an output capable of driving at least three levels indicating respective digital values. A digital control circuit is coupled to the PAM driver and operable to cause the PAM driver to provide a preamble signal before the read clock signal, the preamble signal including an initial toggling state in which the PAM driver toggles between two selected levels at a first rate, and a final toggling state in which the PAM driver toggles between two selected levels at a second rate higher than the first rate, with a length of the initial toggling state and a length of the final toggling state are based on values in a mode register.