Dave, if you want to roll your own get a copy of 'Electronics and Wireless World"
DEC 2001 from yr local library. Page 922 has article 'Differential-in 100Mhz scope probe"
by Cyril Bateman. PC boards would not be available from him now, but his fully specified circuit and construction methods
should help you achieve your aim. and be easily down gradable to your target of 20MHz bandwidth with lower spec'd IC's
Some Specs are :
CMR : < 10Mhz >80dB>,70dB at 10MHz, 49dB at 120MHz (Ref 1V input and 10:1 attenuation set)
MAX4005 used inside the probes,MAX 4144 and MAX4107 used inside the direct input to scope
box. Copper pipe used for probe bodies.
Its also easy to calibrate and adjust. Cyril is (was?) a professional design engineer and a consultant
on capacitor design. He produced quite a few bits of pro spec'd test instrumentation in E&WW and his Cap esr tester is
likely to have been (and still be ) the most accurate esr meter so far ever designed for both enthusiast and semi pro work
I considered getting his PC boards at the time, but got myself a TEK P6046 and amplifier unit which both worked and were in spec
(If you are thinking of buying these be aware that not many are now in fully specified or even in working condition)
John
