[sdiy] CD4051 working as Demux

[Magnus Danielson]

From: Gorka Garcia <torpedo at demadrid.com>
Subject: [sdiy] CD4051 working as Demux
Date: Sun, 13 Feb 2005 11:18:13 -0800 (PST)
Message-ID: <20050213191813.30EF437CEE at sitemail.everyone.net>

> Hello List!!!

Hi Gorka!

> How does the 4051 operate when being used as a Demux? Basically, my concerns
> are about what does it do when more than one channel is selected and when no
> channel is selected. Looking at the datasheet, it does not seem to explain
> much about its functionallity as a demux.

The 4051 has been successfully used as a demux of CV signals in several synths.
Just look at the OB-8 schematics for instance, from each of the 8 taps a 22nF
cap hangs with a TL084 op-amp as a voltage-buffer. By keeping the update rate
sufficiently high, there is no real problem with doing this.

Basically, the 8 analog gates will be high-impedance when they are not enabled
and then only one of them can be enabled at any point in time. The inhibit
input ensures that all 8 gates are in their off-state unless you want one of
them enabled.

Cheers,
Magnus