LM 13600 and 13700

Haible_Juergen#Tel2743 HJ2743 at denbgm3xm.scnn1.msmgate.m30x.nbg.scn.de
Wed Apr 17 23:25:00 CEST 1996


> Just curious, I was looking thru some notes yesterday and the
> LM13600 was mentioned. Was this superseeded by the LM 13700?
> i.e. is the 13700 a reasonable replacement?

No, they have different buffer stages. The '700 has just an emitter
follower. This provides a rather high buffer input impedance, but
yet not enough for some applications. The '600 has the OTA's
control current refleced to the emitter of the darlington's first
transistor. This way the buffer impedance is even *lower* than
in the 13700, but it is *tracking* with the gm of the OTA, which is
a good thing for some filter applications.
The best thing is using an additional FET in front of the internal
buffer for critical designs.

JH.

PS.: Don't use 13600's in Vocoders! The gm control current
reflected to the buffer stage will produce some nasty feedthru
from analysis to synthesis section. 13700's are far better here.



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