Lavry DA2002 Operation Manual - Part Ii: Theory of Operation
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effective adjustment of a part in 5 million per calibration DAC step.
resistor, thus a full 10V swing on the calibration DAC can only pull a given node by +/-4mV, providing an
bit device to ensure monotonic performance. Each DAC is fed to its corresponding node through a large value
measured node. This is done via the calibration 14 bit DACs (see diagram). Each calibration DAC is used as a 13
comparator strobing cycle, the processor decides whether to increase or decrease the specific voltage of the
The strobing is repeated 4000 times for the sake of averaging out any error due to amplifier noise. At the end of a
comparator gain blocks in the simplified diagram). The processor strobes the comparator and reads its output.
greatly amplified and then fed to a strobing comparator (see multiplexers for calibration and error amplifier and
processor the required adjustments. The voltage difference between any given network node and the reference is
A sequence where each resistor is tapped (one at a time) for voltage comparison against a reference level tells the
Calibration
variations.
Keeping the resistors at constant temperature overcomes resistor dependency on environmental temperature
such as a home thermostat is undesirable because it produces turn on and turn off surges-- thus audible kicks.)
networks are kept at a constant temperature by a linearly controlled heating element. (A bang-bang controller,
subject to short term drift due to temperature variations and long term drift due to component aging. The resistor
The PCM DAC is constructed of custom made laser trimmed thin film resistor networks; yet any resistor is
Oven control
The simplified block diagram (figure 1) shows the basic building blocks.
Part II: Theory of operation
Operations Manual
DA2002