ADC gain estimator

The measured sub-exposure signals are in counts, but the detector output is reported in \(adu\). ExoSim simulates the analog-to-digital converter (ADC) with AnalogToDigital, which converts the \(counts\) of the sub-exposures into the \(adu\) of the NDRs (see Analog-to-digital conversion).

The ADC output is an unsigned integer stored in a fixed number of bits. Since it can only represent values up to \(2^{n_{bits}} - 1\), a conversion factor is needed to rescale the floating-point NDRs into that range. This factor is the ADC_gain:

\[g_{ADC} = \frac{2^{n_{bits}}-1 }{ADC_{max}}\]

where \(n_{bits}\) is the number of bits of the ADC and \(ADC_{max}\) is the largest value the ADC should handle. For a 16-bit ADC, \(2^{16} - 1 = 65535\); with a target \(ADC_{max} = 120000\), this gives \(g_{ADC} = \frac{65535}{120000} = 0.546125\).

Set the two parameters in the tool configuration file:

<channel> channel_name
    <detector>
        <ADC_num_bit> 16 </ADC_num_bit>
        <ADC_max_value> 120000 </ADC_max_value>
    </detector>
</channel>