I know you have spend lots of time and efforts, but unfortunately the circuit needs some changes:

1. Input impedance of your circuit is 1MOhm. This is standardly for a scope input. But the buffer following R5 and R6 needs to have a much higher input impedance than what an AD844 can offer. So, please use the FET-buffer at this place, shown in the schematic of bitscope. There's hardly an alternative to such a FET-buffer at this place.

2. If you want to handle a signal range of 0.01V to 5V in 1:2:5 steps, as it common practice with standard scopes, then you need three separate dampening paths in parallel at input of FET-buffer, which provides a dampening of 1, 10 and 100. This also, because the AD844 being used later in the signal chain can only handle signals smaller than +-1V at input. If you take into consideration, that signal can overange the screen in certain cases, than to guarantee proper performance of AD844, input signal at this chip should be even lower.
Only one of the three paths is to be enabled at a time and this by the help of some REED-relays.

3. The offset shifting circuitry arround IC3 will not work properly, because the actual superimposed offset depends on which relay (K4, K5 or K6) is turned-on. So, you should provide the offset shifting in a different way, for instance like bitscope does it.

4. I would suggest the following circuit behind the FET-buffer:

- Connect directly at output of FET-buffer an AD844 with a gain of +2. Take care, for the wanted bandwidth of only 10MHz the capacitor between inverted input of OPamp and signal ground is not needed.

- Behind this AD844 put the circuit which is shown in the schematic of bitscope, where this 1:1, 2:1 and 5:1 dampening (arround MAX4052) can be seen. This circuit will provide the gain switching much easier than a relay circuit.

- At output of MAX4052 put another AD844 with a gain of +10. Again without additional cap between inverting input and signal ground.


Kai