If the effect that Ballegeer Jeffrey is seeing is caused by the transistors not turning off fast enough at the higher frequencies then there is a way to improve the OFF time of the transistor as described previously. Below is a diagram of the connection. Provided the pin that drives the input has a fast fall time and a lower impedance than the input of the base circuit then the diode and capacitor can effectively suck the charge out of the base storage capacitance when the input goes low thus making the NPN transistor turn off faster. If you replace the shottkey diode with a direct wire then the capacitor can also help to improve the turn on time as long as the input signal has good fast rise time and low source impedance. (A typical 8052 pin does NOT meet this criteria). The capacitor value is nominally picked at 10 times the base storage capacitance of the transistor. The diode in the connection can be way more effective if it is a low drop shottkey type.



Note: A Baker clamp is a quite different circuit for a quite different purpose.

Michael Karas