In a message dated 27/05/2010, gmvoeth@........... writes:

Can any  of you do that for me ??
Teach me your solution in terms I
can  understand.



Hi Geoff,
 
    The amount of protection needed to prevent the  current drawn by one IC 
from effecting another depends on what they are doing  and on the 
properties of the circuit. A capacitor also has some internal  resistance and some 
inductance. Some ICs sink supply currents of over an  amp when switching. This 
can effect the voltage supplies to other circuits  due to the resistance of 
the circuit board wiring and the bypass capacity to  earth. It can effect 
the signal and the offset of an opamp - check the  frequency plot of the 
power supply rejection ratio on the data sheet.  Ceramic capacitors and tantalum 
electrolytics have low internal resistances  and can supply large current 
pulses. Aluminium electrolytics and film  capacitors tend to have significant 
internal resistances. 
    It may be practical to insert small resistances in  series with the IC 
supply rails and the bypass capacitors of the switching  circuit. You can 
also add bypass wires in parallel with the supply rail tracks.  This can also 
be done for the input opamp of your amplifier. 
 
    Regards,
 
    Chris Chapman






In a message dated 27/05/2010, gmvoeth@........... writes:
Can any=20
  of you do that for me ??
Teach me your solution in terms I
can=20
  understand.


Hi Geoff,
 
    The amount of protection needed to prevent th=
e=20
current drawn by one IC from effecting another depends on what they are do=
ing=20
and on the properties of the circuit. A capacitor also has some internal=
=20
resistance and some inductance. Some ICs sink supply currents of over =
;an=20
amp when switching. This can effect the voltage supplies to other cir=
cuits=20
due to the resistance of the circuit board wiring and the bypass capacity=
 to=20
earth. It can effect the signal and the offset of an opamp - check th=
e=20
frequency plot of the power supply rejection ratio on the data sheet.=
=20
Ceramic capacitors and tantalum electrolytics have low internal resis=
tances=20
and can supply large current pulses. Aluminium electrolytics and film=20
capacitors tend to have significant internal resistances. 
    It may be practical to insert small resistanc=
es in=20
series with the IC supply rails and the bypass capacitors of the swit=
ching=20
circuit. You can also add bypass wires in parallel with the supply rail tr=
acks.=20
This can also be done for the input opamp of your amplifier. 
 
    Regards,
 
    Chris Chapman