| Products > Test Equipment |
| Siglent SDS1000(X) / SDS2000(X) or LeCroy WaveAce (Blackfin) hacks? |
| << < (3/19) > >> |
| KeBeNe:
here is my HW mod on 2104x, this changed the 3db limit from around 250Mhz to 350Mhz |
| kado:
KeBeNe: can't read the red words in the picture. Did you remove or exchange a cap ? Thanks for a little more information. Karsten Gesendet von iPhone mit Tapatalk |
| markus_jlrb:
FYI, the AD8370 is a low cost, digitally controlled, variable gain amplifier (VGA) http://www.analog.com/media/en/technical-documentation/data-sheets/AD8370.pdf -3dB @ 750MHz, 40dB gain range, serial 8-bit interface (7bits without MSB is gain code) I'm not quite sure if there is a BW restriction by passiv caps. It's more probably that FW influence the max BW. Any comments or expirience on this issue? Markus PS.: see fig. 7 - gain code values. PS2.: Perhaps I'm wrong. The DS describes the influence of the Output C's on page #17++ If a 1nF cap us used instead of 10pF the differenc is round 2.1dB @ 100MHz. So this could be a point to take into account concerning BW max. |
| KeBeNe:
Yes, i have removed this capacitors |
| bugi:
The AD8370 can be used for adjusting the gain (vertical) somewhat smoothly, but, referring to that same fig.7, note how the bandwidth (-3dB relative to the low-frequency level) is almost the same no matter what gain/setting is used. Having such flat response to as high a bandwidth as possible independent of the gain setting is actually intended for a typical VGA. (Also note, the page 17 talk on capacitors is about connecting the input signal in AC-coupled mode through caps; in an oscilloscope the connection would likely be DC coupled. Some other arrangement a little bit away from the VGA would be used for bandwidth limit, especially considering that "care must be taken to minimize parasitic capacitance on the input and output. The AD8370 could become unstable with more than a few pF of shunt capacitance on each input".) |
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