AME7106 Datasheet, PDF (8/20 Pages) Analog Microelectronics – 3-1/2 Digit A/D Converter High Accuracy, Low Power

AME, Inc.
AME7106/AME7106A/AME7106R
AME7107/AME7107A/AME7107R
The A/D conversion has the following three phases:
1. Auto-Zero Phase
2. Integration Phase
3. De-integration Phase
Auto-Zero Phase
The INHI and INLO are shorted to analog common in-
ternally. The reference capacitor is charged to the ref-
erence voltage. A feedback loop is closed around the
system to cancel the offset voltage of buffer, integrator
and comparator.
Signal Integration phase
The converter integrates the differential voltage across
the INHI and INLO for a fixed time, 1000 system clocks.
The polarity of the signal is determined at the end of
this phase.
Reference Integration Phase
INLO is internally connected to the Analog Common,
INHI is connected across the reference capacitor with
appropriate polarity determined by the control circuit.
The integrator output will then return to zero. The time
it takes to return to zero, 1000 X VIN /VREF, is the
digital representation of the analog signal.
Differential Signal Inputs (INHI & INLO)
The AME7106/AME7107 has true differential inputs and
accepts input signals within the input common mode
voltage range (Vcm). Typical range is from 1V above
the V- to 1V below the V+. The integrator output can
swing within 0.3 V of V+ or V- without increasing
3-1/2 Digit A/D Converter
High Accuracy, Low Power
linearity errors. Care must be exercised to make sure
the integrator output does not saturate. In a typical
application, the common mode is eliminated by con-
necting the INLO to COM, Analog Common.
Differential Reference (VREF+ & VREF-)
The reference voltage can be generated anywhere
within the V+ to V-. Under a large common mode volt-
age, reference capacitor can gain charge during the
de-integration of a positive signal. The reference ca-
pacitor will lose charge when de-integrating a negative
input signal. The difference in reference voltage for
positive or negative input voltages can cause the
rollover error. To prevent rollover error from being in-
duced by large common-mode voltages, reference ca-
pacitor should be large compared to stray node capaci-
tance.
Analog Common (COM)
The Analog Common is to set a common mode volt-
age for the analog signal. The analog common is typi-
cally 3.0V below V+, set primary for the battery oper-
ated application. Analog common is capable to sink 20
mA. It’s source current is limited to 10 µA. Analog
common is therefore easily pulled to a more negative
voltage to override the internal reference. When sup-
ply voltage is greater than 7V, analog common can be
used as reference source with temperature coefficient
of typically 50 ppm/^OC. The internal heating by the LED
display drivers of the AME7107 may degrade the sta-
bility of the Analog Common. An external reference is
recommended.
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