Bruce, That is at first counterintuitive (conventional wisdom and good design practice suggests good decoupling caps across the supply pins), but it makes perfect sense.
I have to try this (a small resistor in series with the positive supply rail) when I get home. Thanks for the tip. Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -----Original Message----- From: Bruce Griffiths <[email protected]> Sender: [email protected] Date: Wed, 11 Jan 2012 07:30:27 To: Discussion of precise time and frequency measurement<[email protected]> Reply-To: Discussion of precise time and frequency measurement <[email protected]> Subject: Re: [time-nuts] Temperature and signal amp for 'Bay FE-5680A? David wrote: > On Tue, 10 Jan 2012 21:57:49 +1300, Bruce Griffiths > <[email protected]> wrote: > > >> Hal Murray wrote: >> >>> The TADD-3 uses 3 AC drivers in parallel, each going through a 51 ohm >>> resistor. Changing those resistors to 150 ohms should work. Maybe a bit >>> lower to account for the impedance in the drivers. I'd probably check it >>> with a scope. >>> >>> >> That approach doesn't do anything for the Vcc and GND bounce exhibited >> by the driver chip. >> GND and Vcc bounce is the cause of the high frequency ringing exhibited >> by the TADD-3 outputs. >> This ringing can even be observed at the outputs of inverters whose >> inputs are tied low or high in the same package >> >> Damping the crossover current induced transient in the supply leads >> (bondwire and lead frame) inductance is one way to minimise this. >> A small resistor in series with the Vcc pin often works well, the >> resistor value being chosen for near critical damping. >> >> Another problem with the TADD-3 is the sharing of a driver chip by >> different input frequencies which leads to intermodulation between the 2 >> outputs. >> > I have never seen that much ground bounce before so assumed it was a > termination problem. Was the driver chip decoupling inadequate? That > at least would be easy enough to fix. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > No, its due to the high switching speed of the output stage. Such ground bounce is typical for ACMOS devices without a staged output device turn on. Low inductance decoupling has no effect on internal bondwire and leadframe inductance. Apart from redesigning to chip to have a more gradual output stage turn on, damping of the circuit is the only effective cure. An example of the effectiveness of this can be found in the SRS FS730 distribution amplifier CMOS output option. Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
