Re: [softrock40] Newbe question LO clock jitter.
- On 1 Jan 2008 at 13:35, g0opb wrote:
> Hi all,You can get 74AC parts that are pin for pin compatible and even available
> I have trawlled through all the files and posts (before getting
> too bored) and can find no referance to LO clock jitter. I note some
> ccts use D type flip flops with hysteresis in an attempt to make the
> edges faster! but this makes the problem even worse as the threshold
> voltages can move around significantly.
> Why am I concerned...about to order a softrock IF kit to play with and
> I dont think 74HC/T logic is fast enough when operating with a 32.5MHz
> clock (4X my RX 8.125Mhz IF).
> There is also a need to maintain a consistant Mark/Space ratio for any
> software I/Q gain-phase correction system to work correctly.
> Am I missing something, or is this a second order effect compared to
> other system limitations, like jitter may be completly swamped by my RX
> PLL 1st LO noise performance!
> Tony G0OPB
in DIP packages. You can also get 74LVC parts in SOIC that are even
faster. Both are available from Mouser and DigiKey. A 74AC74 typically
clocks to 125 MHz and a 74LVC74 can go to 150 MHz(but operates at 3.3V)
Dave - WB6DHW