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.
