How can I drive an IGBT?

What makes you think adding an IGBT will cause the "signal (to) drop down to certain level."? The IGBT's capacitive gate will *slow* down the gate-drive signal, but after an RC-style delay it'll be as large as before. Lots of applications don't mind a slow switching time. Another point, IGBT gates have much less capacitance than FET gates, for parts with equal high-current capability, which reduces any issues arising from this problem. This said, the 20mA bipolar output drive from an opamp, like an LM324 or LM358, exceeds the drive available from a comparator.

A typical low-current IGBT might be the HGTP3N60A4D (rated at 8A and 600V), or the IRG4BC10K (rated at 5A and 600V). The latter IGBT has 220pF of Ciss gate capacitance, and requires about 10nC to change switching states (fig 8). This means that a 20mA drive could switch an irG4bc10k IGBT in less than t = dV C / I = 100ns ahem, assuming the IGBT can respond that fast. You can use this basic principle to evaluate your design.

And, I should add, to conclude that for simple on/off operations with a small IGBT like this, the lower-current gate drive from a comparator should be fine. For example, 5mA drive would provide a 0.4us on/off switching speed, which is plenty fast for a motor.