Cirrus Logic CS5374 - Manual (Page 17)

CS5374
CS5374
17
selected differential input signal, and will vary as
the signal common mode varies. The GUARD out-
put will not drive a significant load, as it can only
provide a shielding voltage.
3.3 Differential Signals
Analog signals into and out of the amplifiers are
differential, consisting of two halves with equal but
opposite magnitude varying about a common mode
voltage.
A full-scale 5 V
pp
differential signal centered on a
–0.15 V common mode can have:
SIG+ = –0.15 V + 1.25 V = 1.1 V
SIG– = –0.15 V – 1.25 V = –1.4 V
SIG+ is +2.5 V relative to SIG-
For the reverse case:
SIG+ = –0.15 V – 1.25 V = –1.4 V
SIG– = –0.15 V + 1.25 V = 1.1 V
SIG+ is –2.5 V relative to SIG-
The total swing for SIG+ relative to SIG– is
(+2.5 V) – (–2.5 V) = 5 V
pp
. A similar calculation
can be done for SIG– relative to SIG+. Note that a
5 V
pp
differential signal centered on a –0.15 V
common mode voltage never exceeds 1.1 V and
never drops below –1.4 V on either half of the sig-
nal.
By definition, differential voltages are to be mea-
sured with respect to the opposite half, not relative
to ground. A multi-meter differentially measuring
between SIG+ and SIG– in the above example
would properly read 1.767 V
rms
, or 5 V
pp
.