An implantable pulse generator (IPG) that generates spinal cord stimulation signals for a human body includes a timing generator and high frequency generator. The timing generator generates timing signals that represent stimulation signals for multiple channels. The high frequency generator determines whether to modulate the timing signals and modulates them at a burst frequency according to stored burst parameters if the decision is yes. As such, the IPG provides the ability to generate both the low frequency and high frequency stimulation signals in different channels according to user programming.