PicoScope 7 Software
Available on Windows, Mac and Linux
Thanks for the info.Martyn wrote:Take a look at 4000 series which are 12 bit, or the 16 bit PicoScope 4262 which is designed for audio applications.
Additionally there are the flexible resolution 5000 series which can switch between 8/12/14/15/16 bits depending upon number of active channels and speed of sampling required.
Gerry wrote:Hi Ben321,
There is no extra filter in the signal path.
In the industry of Data Acquisition, the manufacturers goals are to provide a well specified, high quality instrument at a cost-effective price. When designing with ADC's you do indeed need to avoid aliasing and other phenomena that will degrade the performance of the product. However, multiple pre-digitisation anti-aliasing filters (for each channel) that track every selected sample rate, taking into account the resolution (detectable levels of aliasing), incorporate some form of switching for when ADC's are stacked, and other considerations are going to add significant cost to the product. Then there is the consideration of filter characteristics, and what you are forgetting is that with a filter cut-off at the bandwidth limit (-3dB), you still need some frequency range to actually roll-off the signal before it reaches the stop-band level (you can't get an analog brick-wall filter). So, Nyquist may theoretically be a desirable limit, but is not possible to achieve in practice in an analog front-end anti-aliasing filter. Also, with a filter you need to consider pass band ripple, and phase distortion that can affect signal quality (and in audio, which is a common application for our PicoScope 4262, it's important to avoid distortion that causes group phase delays for quality audio reproduction).
Then there is the matter of displaying the signal once you have captured the data, and in this respect limiting to just below the Nyquist frequency is not sufficient because you need more data points to be able to reconstruct the signal with any accuracy (there are numerous sources on the internet that explain this in more detail).
So what you will find is that manufacturers tend to prefer specifying a more restricted bandwidth in order to provide sufficient frequency range for the highest bandwidth signal to be naturally rolled off by the time the Nyquist frequency is reached, and to be able to correctly display the data. So we tend to aim for a sample rate that is about 5 times the maximum expected bandwidth, with some slight variations (other manufacturers may have different ratios). This allows our customers to achieve their bandwidth target with the correct selected PicoScope, while making a measurement that still meets the quality parameters mentioned in our specifications, without paying a small fortune for the privilege.
That said, we have customers with very specific needs that take it upon themselves to buy anti-aliasing filters to apply to their signal before measurement with a PicoScope in order to give them extreme quality sampling, for the measurements that require it. Of course, you can buy Oscilloscopes with anti-aliasing filters inside, but they tend to be much more expensive pieces of equipment.
Regards.
Gerry
8 bits scopes don't work too well, because the brightness range for an ntsc signal includes levels that are "darker than black" which are used for blanking (turning off the electron gun) and for sync (both horizontal and vertical). If you want 8 bits for brightness (displayable light levels) in the image portion of the signal you'll still need more bits to take into account the sync levels. The scope must have at least 9 bits per sample for my intended use. And to save money, it should have a sample rate no higher than twice the bandwidth.bennog wrote:Ben,
Reading your post I remembered seeing something a while ago. (ok a long while ago )
topic11185.html
And the result.
http://codeandlife.com/2012/07/31/realt ... picoscope/
And in color
http://codeandlife.com/2012/09/12/color ... ope-3206b/
http://codeandlife.com/2012/10/09/compo ... -practice/
This is done with a 8 bit version of the scope
Benno