SSM2110_15 Datasheet, PDF (9/11 Pages) Analog Devices – TRUE RMS TO DC CONVERTER

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FIGURE 9: Error Trimming
ERROR TRIMMING
The offset, reference and scale factor trims (Figure 9) can be
used to improve the overall accuracy of the device. The correct
procedure for trimming outthe various errors is as follows. First,
+LOG IN (pin 10) and -LOG IN (pin 11) should be connected to
V REF(pin 3). The offset trim should be adjusted to achieve OV at
the V LOG(RMSo)utput. This nulls out any DC errors due to offsets
in the log recovery amplifier. Second, reconnect the f:LOG IN
pins as shown in Figure 9. Apply an input signal of 1OOmV RMS
(1 O~ARM_!»A' djust the reference trim to obtain OVat the V LOG(RMS)
recovery amplifier and other errors. It sets the reference current
to 10f.1A.Third. change the input signal to 1VR'-AS(1 OO!lARMS)'
Adjustthe scale trim to obtain 1.OODVat the VLOG(RMSou) tput. This
adjusts the scale factor to obtain 1V/20dB (50mV/dB). If other
reference currents or scale factors are used then steps 2 and 3
will have to be changed accordingly.
This same procedure can be used for the log absolute value and
log average absolute value configurations. If the log recovery
amplifier is not used then the circuit in Figure 10 should be used
to trim the offsets.
output. This compensates for the input bias current of the log