iC-TW8 16-BIT SIN/COS INTERPOLATOR
Serial Configuration Mode
Jan 9, 2013 Page SC13/36
Single-ended Sin/Cos inputs can also be connect-
ed to the iC-TW8 by connecting the SIN– and
COS– pins to the proper bias voltage as shown in
Figure 13. Since the iC-TW8 provides high-
impedance signal inputs, a simple resistive volt-
age divider can be used to generate the required
bias voltage. For AMR sensors, it is recommend-
ed that the resistors of the bias generator match
the AMR sensor bridge resistance to improve
power supply noise rejection. No decoupling ca-
pacitor should be used.
Connecting an Index Sensor (If Used)
The iC-TW8 can interface to a wide range of index
sensors or gating sources to provide an index or Z
output which is synchronized with the AB outputs.
Digital Hall sensors are often used for this purpose, as
shown in Figure 14.
VDD
iC-TW8
ZERO+
VDD
AVDD
SIN+
ZERO-
Digital Hall
active low
Sensor Bridge 0
COS+
Figure 14: Digital Index Sensor Connection
Sensor Bridge 1
Digital sensors (Hall, MR, and others) typically pro-
vide an active-low signal via an open-drain output that
pulls low in the presence of a magnetic field. Connect
an active-low (open drain) digital index sensor to the
iC-TW8 ZERO– input (pin 48) and connect the
ZERO+ input (pin 47) to a resistive voltage divider set
to the midpoint of the index sensor output voltage
swing to provide good noise rejection. For active-high
(open source) digital index sensors, reverse the
ZERO+ and ZERO– connections.
SIN-
COS-
iC-TW8
Resistive Bias
Generator
Figure 13: Single-ended Sensor Connection
Differential inputs should be used whenever pos-
sible to reject common mode distortions and pro-
vide increased signal amplitude and improved
signal to noise ratio (SNR).
Analog-output index sensors, such as MR bridges, can
also be used with the iC-TW8 in serial configuration
mode as shown in Figure 7.
Regardless of input configuration, the auto-
calibration feature of the iC-TW8 is sufficient in
most cases to compensate for any signal offset,
gain, and phase distortions without requiring any
additional external components.
iC-TW8
ZERO+
ZERO-
MR Index
Sensor
Figure 15: Analog Index Sensor Connection
If no index (Z) output is required, connect ZERO+
(pin 47) to ground and ZERO– (pin 48) to AVDD.
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