Differential Probe for Oscilloscopes
Probes for oscilloscopes are easier to build than most people beleive!
The differential probe described here roughly features the following parameters:
Attenuation: -20dB (1/10)
Input impedance: 390K
Bandwidth: 80MHz (provided a good layout is used)
Maximum differential input voltage (begins clipping): 20V
Special care must be taken for propper layout. It must be absolutely
symmetrically in the RF part (IC3, Q2, Q3, R10, R11, R14, R15, R17, R18,
R6, R7). Ground should be routed exactly on the symmetry line. A
printed board is not mandatory (I used a simple hand wired evaluation board
and only used a very wide wire for ground to minimize degradation due to
skin effect). Blocking capacitors C10 and C11 must be placed as close to
IC3 as possible.
The component list