4 TECHNICAL DATA
4.2.6 Description of adjustable settings
The output incremental and reference signals of the METIRIO Encoder can be adjusted by switch-
ing the setpoints of the functional blocks. The functional blocks of the integrated circuit are ad-
justable via I
2
C interface by writing values into specific registers. These registers contain several
digital values that define analog settings and can thus be used to configure and optimize the en-
coder’s signals. A detailled description of the registers and the I
2
C protocoll description can be
found in the user guide OE-UG00001. In the following sections of this user manual a description
of each block’s functionality and the electronic specifications are given, without additionally going
into the specific register and interface description.
Signal strength adjustment
Table 4.5: LED block
Parameter Test Conditions/Comment Min. Typ. Max. Unit
LED control mode (Register 0x0208 with D1=0)
LED current under various optical conditions 8 15 31 mA
Resolution 6 bit DAC 63 Steps
LED control mode (Register 0x0208 with D1 =0)
Step size 0.47 mA
Differential nonlinearity -0.2 0.2 LSB
Integrated nonlinearity -0.7 0.1 LSB
LED loop mode enabled (Register 0x0208 with D1=1)
Voltage Setpoint sum of TIA outputs 1.2 2.4 V
Resolution 6 bit DAC 63 Steps
Step size 19 mV
The Encoder output signal depends on the mechanical setup and the LED power. LED current can
be set up to max. 30 mA in 0.47 mA steps. The amplitude of the analog output signals increase
proportional to the LED current. For best Signal to Noise ratio it is recommended to set the output
amplitude as good as possible by tuning the LED current.
Besides controlling the LED current with a fixed value it is possible to enable a regulation loop
for the LED current. With loop-mode enabled the brightness of the light source will be adapted
automatically by the encoder in order to maintain a constant illumination on the diode array. The
actual value of the loop is the sum of all TIA outputs which is compared to a setpoint given by the
LED-DAC register. The LED-DAC register value behave proportional to the LED current and the TIA
output voltage. In the case of instability it is possible to change the loop gain by setting the LED-CS
register. The loop bandwidth can be reduced with the LED-speed-ctrl register.
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