| ??? 01/13/06 17:31 Modified: 01/13/06 17:33 Read: times |
#107324 - Corrected mistakes Responding to: ???'s previous message |
To implement this is very easy. You just have to add a big offset. On the other hand, then your signal will clip somewhere in your circuit. So, you need a circuit, which can easily be overdriven without corrupting the signal in the seen window. This means some intensive designing and testing, but is possible. So it wouldn't be easy. Since you have a lot of experience using Scopes did you used this feature so far ? If this is an important feature so maybe it would worth to implement. Yes, grounding is always good in HF circuits... I have a question in my mind, Consider we want to fed a signal from our MCU to an analog cihp like 4052. Here Current will flow from Digital VDD to the Analog Ground. Is this alright or we have to use a buffer here ? Take care, this is not a standard procedure to increase bandwidth with HF OPamps, but will very probably result in wild oscillations and heavy instability! Connecting caps in the feedback loop is a big no no, when working with HF OPamp. Datasheet of AD844 only recommends this for high gains, at about 100 or so. Then this cap can help a bit. But if you connect it at gains lower than 100, then instability will occur.
There's no need for this capacitor at gains like 2 and 10. By the way, if you have a look at figure 11, 16 and 21, then you will notice, that there's already a peak in the gain versus frequency plot. This is an indication that the additional cap would result in a disaster. So, please omit it! Thanks for the detailed explanations.I just removed these in the new schematic. Anyhow you produce the offset voltage there, you should have caps connected to ground as it's shown at the bitscope's schematic. Sorry I just forgot them.I included them in the new schematic but I opt the Op-Amp suggestion so they are not in the new schematic. Is the offset circuit alrigt ? But, again, don't forget the caps to ground. I placed those Caps between the Inverting input to the ground. Did i do what you meant ? BF245B seems to fit well. Do select them in pairs, though, as mentioned at bitscope's schematic. I'll try to find the best ones , and as Bitscope author says I'll try to measure the Ids with Vgs=-0.6 to find a matched pair. - At output of FET-buffer should not sit an inverting OPamp, as you have drawn it, but only a non-inverting! That was a mistake ,C10 also Corrected in the new schematic. Shift+Refresh ;) http://www.8052.com/users/far...pdated.GIF Thanks again, |
