An On-Screen-Display (OSD) insert circuit includes an OSD signal generator
for generating a switching signal and an analog additional image signal
based on a first clock signal, an analog-to-digital converter for
converting the generated additional image signal into a digital
additional image signal based on a second clock signal as a sampling
clock signal, a switching circuit for switching between a digital video
signal and the digital additional image signal based on the switching
signal, and a control-signal generator operable to generate the second
clock signal. The digital video signal has a horizontal synchronizing
signal. The control-signal generator is operable to reset the first clock
signal with a signal having a predetermined phase difference including
zero with reference to the horizontal synchronizing signal, and to
generate the second clock signal so that a phase of the second clock
signal is adjusted with respect to the horizontal synchronizing signal.
This OSD insert circuit can insert the analog additional image signal
into the digital video signal without converting the digital video signal
into an analog signal.