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Page 51 of 97
Issue: 1.04
6 The microK Technology
The microK uses a number of new technologies and measurement techniques to
achieve performance that has not previously been available with potentiometric
measurement systems.
6.1 The ADC
The ADC (Analogue-to-Digital Converter) in a precision instrument is the
‘measurement engine’. Its performance is the starting point for achieving low
measurement uncertainty. The microK uses a completely new type of ADC,
which was designed specifically for this product. It is based on the well
established
Σ
-
∆
(sigma-delta) technique but uses multi-bit feedback to achieve
performance that is not achievable with conventional
Σ
-
∆
ADCs.
In a conventional
Σ
-
∆
ADC, the analog input signal is subtracted from the output
of a 1-bit DAC before being filtered by a series of cascaded integrators. The
signal then passes to a 1-bit ADC that drives the DAC and forms a feedback loop
Integrators
1-Bit DAC
INPUT
Digital
Filter
OUTPUT
VALUE
1-Bit ADC
Conventional
Σ
-
∆
ADC
The extremely high, low-frequency loop-gain of the cascaded integrators ensures
that the input signal is balanced against the output of the DAC so that the average
value of the 1-bit data stream from the DAC equals the input signal. A low-pass
digital filter is then used to extract the converted value from the 1-bit data
stream.
