一个open loop two stage amplifier 就是comparator了阿。。。first stage...differential input amplifier.. second stage common source amplifier。。你要hysteresis吗??如果要你就要用positive feedback了。。主要还是看你的design spec要快的。。propagation delay in few nsec的。。你可以考虑加个high bandwidth, low gain preamplifier。。。