• True differential input (or maybe I should say isolated ground ?)
Differential inputs were a rare built in feature even in the past and even then, differential probes were available. Today this feature is provided by differential probes.
Using two channels in add and invert mode can work with a modern DSO although usually not as well as an analog oscilloscope because of increased quantization noise. (1) This is one place where increased digitizer resolution would make a significant improvement but most people just use a differential probe.
Isolated inputs are a different thing and very useful. Many modern DSOs support this but it is somewhat of a specialized feature. I suspect most users who require a differential probe would do better with isolated inputs. Compared to a differential input:
- Built In
- Lower Noise
- Higher and More Reliable Common Mode Rejection
- Higher Bandwidth
- Low Common Mode Impedance - This is worse than with a differential input but not usually a problem.
• >8 bit resolution A/D (10 or maybe 12 seems MUCH better)
Greater than 8 bit resolution is of limited use. Vertical channel accuracy, linearity, settling time, and noise usually make 8 bits more than enough unless bandwidth is severely restricted.
• >500 MS/sec when all channels are in use (reasonable glitch capture requires about 10 sample per repeating time period)
Lots of DSOs meet this requirement. Even lots of 30 year old DSOs meet this requirement.
I would think that all of those feature could be added for a $100-$200 dollar. Of course the question always is, will the public pay that ?
It is not about the cost to implement these features. It is about what customers will pay for them.
A majority of customers will pay that much for a change in style and features which make a DSO worse. Low contrast user interface and controls? They have that. Want a glossy screen which reflects the room lights into your face? You are in luck.
(1) Some early DSOs used analog channel switches so do not suffer any increase in quantization noise making them particularly suited to add and invert differential operation. These DSOs are a little weird; when the common mode rejection is adjusted in add and invert mode, you can visibly see the trace noise eerily decrease.