Cirrus Logic CS3301A - Manual (Page 10)

CS3301A
10 DS757F1
2.1.3 Differential Signals
Analog signals into and out of the CS3301A are
differential, consisting of two halves with equal but
opposite magnitude varying about a common mode
voltage.
A full scale 5 Vpp 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 multimeter differentially measuring
between SIG+ and SIG- in this example would
properly read 1.767 V
rms
, or 5 V
pp
.
2.2 Digital Signals
2.2.1 Clock Input
The clock signal is used by the chopper-
stabilization circuitry of the amplifier analog in-
puts. The CLK pin can be driven by an external
clock source for synchronous operation, or CLK
can be grounded to run from its own internally gen-
erated clock signal. The CLK pin is connected to a
clock detect circuit which will disable the internal
clock and use an external clock if one is supplied.
If the internal clock signal is to be used, the CLK
pin should be connected to GND.
2.2.2 Gain Selection
The CS3301A supports gain ranges of x1, x2, x4,
x8, x16, x32, and x64. They are selected using the
GAIN0, GAIN1, and GAIN2 pins as shown in
Table 1 on page 7 .
2.2.3 Mux Selection
The analog inputs to the amplifier are multiplexed,
with external signals applied to the INA+, INA- or
INB+, INB- pins. An internal termination is also
available for noise tests. Input mux selection is
∆Σ
Modulator
Test
DAC
Digital Filter
AMP
Differential
Sensor M
U
X
µController
or
Configuration
EEPROM
System
Telemetry
CS3301A
CS3302A
CS5378
CS5373A
Figure 4. Single-Channel System Architecture