timing bug--Ch B vs Ch A

Channel B is delayed relative to A, at low signal levels. To observe this, one needs to send a large signal to Ch A, and trigger on Ch A. Attenuate the signal by 60db and connect it to Ch B. Keep zooming the vertical axis of B, and the signal will shift by about 250ns (90 degrees at 1Mhz).

If you sweep the frequency, put the scope in gain phase mode, and B phase will be linear
In frequency.

The two setup files (*.apc) demonstrate the problem. The differ only in the y-axis zoom on Ch B.

Phase_bug.doc shows the hardware setup with the attenuator connections.

Channel B is delayed relative to A, at low signal levels. To observe this, one needs to send a large signal to Ch A, and trigger on Ch A. Attenuate the signal by 60db and connect it to Ch B. Keep zooming the vertical axis of B, and the signal will shift by about 250ns (90 degrees at 1Mhz). If you sweep the frequency, put the scope in gain phase mode, and B phase will be linear In frequency. The two setup files (*.apc) demonstrate the problem. The differ only in the y-axis zoom on Ch B. Phase_bug.doc shows the hardware setup with the attenuator connections.

At very low levels (5mV and less) we automatically turn on filters to reduce visible noise. To maintain phase coherence, use Settings/Acquisition Settings and turn off the filters. The low level signal will get a bit noisier as a result.

At very low levels (5mV and less) we automatically turn on filters to reduce visible noise. To maintain phase coherence, use Settings/Acquisition Settings and turn off the filters. The low level signal will get a bit noisier as a result.