  Cold atom interferometers have matured to a powerful tool in fundamental
physics research, and they are currently on their way from realizations in the
laboratory to applications in the real world. The radio frequency (RF)
generator is an indispensable component to control lasers and then manipulate
atoms. We developed a highly compact RF generator for fast switching and
sweeping frequencies/amplitudes of atomic interference pulse sequences.
Multi-channel RF signals are generated by using a field-programmable gate array
(FPGA) to control eight direct digital synthesizers (DDSs). We further proposed
and demonstrated a method of preloading the parameters of all RF pulse
sequences to the DDS registers before the execution of the pulse sequences,
which eliminates the data transfer between the FPGA and DDSs to change RF
signals and thus sharply shortens the delay of frequency switching when the
pulse sequences are running. The characterized performance shows the generated
RF signals achieve 119 ns frequency switching delay, and 40 dB harmonic
rejection ratio. The generated RF pulse sequences are applied to a cold
atom-interferometer gyroscope, and the contrast of atomic interference fringes
reaches 38%. This compact multi-channel generator with the fast
frequency/amplitude switching or/and sweeping capability has beneficial
applications for the real-world atom interferometers.
