Cirrus-logic CS5374 Manual de usuario descargar pdf (Pagina 17)

CS5374

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

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

. A similar calculation

can be done for SIG– relative to SIG+. Note that a

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

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Cirrus-logic CS5374 Manual de usuario Pagina 17