Difference between revisions of "HFI time response model"
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===Data compression=== | ===Data compression=== |
Revision as of 17:19, 30 January 2013
Contents
Detection chain[edit]
(Francesco Piacentini)
This entire section has been moved to this page.
Data compression[edit]
The output of the readout electronics unit (REU) consists of one value for each of the 72 science channels for each half-period of modulation. This number, , is the sum of the 40 16-bit ADC signal values obtained within the given half-period. The data processor unit (DPU) performs a lossy quantization of .
We define a compression slice of 254
values, corresponding to about 1.4 s of observation for each detector and to a strip of sky about 8 degrees long. The mean of the data within each compression slice is computed, and data are demodulated using this mean:
where
is the running index within the compression slice.The mean
of the demodulated data is computed and subtracted, and the resulting data slice is quantized according to a step size Q that is fixed per detector:
This is the lossy part of the algorithm: the required compression factor, obtained through the tuning of the quantization step Q, adds a measure of noise to the data. Assuming Gaussian white noise with standard deviation CPV phase after subtraction of the signal from the timeline.
, a quantization setting of /Q = 2 adds 1% to the noise (Pajot et al. 2010; Pratt 1978). The value of was determined at the end of theThe two means
and are computed as 32-bit words and sent through the telemetry, together with the values. Variable-length encoding of the values is performed on board, and the inverse decoding is applied on ground.
Optimal use of the bandpass available for the downlink (75 kb/s
average for HFI science) was obtained initially by using a value
of Q = /2.5 for all bolometer signals.
After 12 December 2009, only for the 857 GHz detectors, the
value was reset to Q = /2.0 to avoid data loss
due to exceeding the limit of downlink rate.
Time response[edit]
The HFI bolometers and readout electronics have a finite response time to changes in incident optical power. The bolometers are thermal detectors of radiation whose response time is determined by the thermal circuit defined by the heat capacity of the detector and thermal conductivity.
Due to Planck's nearly constant scan rate, the time response is degenerate with the optical beam. However, because of the long time scale effects present in the time response, the time response is deconvolved from the data in the processing of the HFI data (see TOI processing).
The time response of the HFI bolometers and readout electronics is modeled as a Fourier domain transfer function (called the LFER4 model) consisting of the product of an bolometer thermal response and an electronics response .
LFER4 model[edit]
If we write the input signal (power) on a bolometer as HFI the bolometer transfer function is modelled as the sum of 4 single pole low pass filters: The modulation of the signal is done with a square wave, written here as a composition of sine waves of decreasing amplitude: where we have used the Euler relation and is the angular frequency of the square wave. The modulation frequency is and was set to Hz in flight. This signal is then filtered by the complex electronic transfer function . Setting: we have: This signal is then sampled at high frequency ( ). is one of the parameters of the HFI electronics and corresponds to the number of high frequency samples in each modulation semi-period. In order to obtain an output signal sampled every seconds, we must integrate on a semiperiod, as done in the HFI readout. To also include a time shift , the integral is calculated between and (with period of the modulation). The time shift is encoded in the HFI electronics by the parameter , with the relation .
the bolometer physical impedance can be written as: where is the angular frequency of the signal and is the complex intrinsic bolometer transfer function. ForAfter integration, the
-sample of a bolometer can be written as whereThe output signal in equation eqn:output can be demodulated (thus removing the
) and compared to the input signal in equation bol_in. The overall transfer function is composed of the bolometer transfer function and the effective electronics transfer function, :The shape of
is obtained combining low and high-pass filters with Sallen Key topologies (with their respective time constants) and accounting also for the stray capacitance low pass filter given by the bolometer impedance combined with the stray capacitance of the cables. The sequence of filters that define the electronic band-pass function are listed in table table:readout_electronics_filters.Parameters of LFER4 model[edit]
The LFER4 model has are a total of 10 parameters(
, , , , , , , , , ) 9 of which are independent, for each bolometer. The free parameters of the LFER4 model are determined using in-flight data in the following ways:- REU setting. is fixed at the value of the
- CPV. is measured during the QEC test during
- , , , are fit forcing the compactness of the scanning beam.
- , , are fit by forcing agreement of survey 2 and survey 1 maps.
- The overall normalization of the LFER4 model is forced to be 1.0 at the signal frequency of the dipole.
The details of determining the model parameters are given in (reference P03c paper) and the best-fit parameters listed here in table table:LFER4pars.
HFI electronics filter sequence[edit]
Filter | Parameters | Function |
---|---|---|
0. Stray capacitance low pass filter | ||
1. Low pass filter | nF |
k |
2. Sallen Key high pass filter | 3 | |
3. Sign reverse with gain | ||
4. Single pole low pass filter with gain | nF |
k|
5. Single pole high pass filter coupled to a Sallen Key low pass filter | k nF k F |
k
Bolometer | (s) | (s) | (s) | (s) | (s) | (s) | ||||
100-1a | 0.392 | 0.01 | 0.534 | 0.0209 | 0.0656 | 0.0513 | 0.00833 | 0.572 | 0.00159 | 0.00139 |
100-1b | 0.484 | 0.0103 | 0.463 | 0.0192 | 0.0451 | 0.0714 | 0.00808 | 0.594 | 0.00149 | 0.00139 |
100-2a | 0.474 | 0.00684 | 0.421 | 0.0136 | 0.0942 | 0.0376 | 0.0106 | 0.346 | 0.00132 | 0.00125 |
100-2b | 0.126 | 0.00584 | 0.717 | 0.0151 | 0.142 | 0.0351 | 0.0145 | 0.293 | 0.00138 | 0.00125 |
100-3a | 0.744 | 0.00539 | 0.223 | 0.0147 | 0.0262 | 0.0586 | 0.00636 | 0.907 | 0.00142 | 0.00125 |
100-3b | 0.608 | 0.00548 | 0.352 | 0.0155 | 0.0321 | 0.0636 | 0.00821 | 0.504 | 0.00166 | 0.00125 |
100-4a | 0.411 | 0.0082 | 0.514 | 0.0178 | 0.0581 | 0.0579 | 0.0168 | 0.37 | 0.00125 | 0.00125 |
100-4b | 0.687 | 0.0113 | 0.282 | 0.0243 | 0.0218 | 0.062 | 0.00875 | 0.431 | 0.00138 | 0.00139 |
143-1a | 0.817 | 0.00447 | 0.144 | 0.0121 | 0.0293 | 0.0387 | 0.0101 | 0.472 | 0.00142 | 0.00125 |
143-1b | 0.49 | 0.00472 | 0.333 | 0.0156 | 0.134 | 0.0481 | 0.0435 | 0.27 | 0.00149 | 0.00125 |
143-2a | 0.909 | 0.0047 | 0.0763 | 0.017 | 0.00634 | 0.1 | 0.00871 | 0.363 | 0.00148 | 0.00125 |
143-2b | 0.912 | 0.00524 | 0.0509 | 0.0167 | 0.0244 | 0.0265 | 0.0123 | 0.295 | 0.00146 | 0.00125 |
143-3a | 0.681 | 0.00419 | 0.273 | 0.00956 | 0.0345 | 0.0348 | 0.0115 | 0.317 | 0.00145 | 0.00125 |
143-3b | 0.82 | 0.00448 | 0.131 | 0.0132 | 0.0354 | 0.0351 | 0.0133 | 0.283 | 0.00161 | 0.000832 |
143-4a | 0.914 | 0.00569 | 0.072 | 0.0189 | 0.00602 | 0.0482 | 0.00756 | 0.225 | 0.00159 | 0.00125 |
143-4b | 0.428 | 0.00606 | 0.508 | 0.00606 | 0.0554 | 0.0227 | 0.00882 | 0.084 | 0.00182 | 0.00125 |
143-5 | 0.491 | 0.00664 | 0.397 | 0.00664 | 0.0962 | 0.0264 | 0.0156 | 0.336 | 0.00202 | 0.00139 |
143-6 | 0.518 | 0.00551 | 0.409 | 0.00551 | 0.0614 | 0.0266 | 0.0116 | 0.314 | 0.00153 | 0.00111 |
143-7 | 0.414 | 0.00543 | 0.562 | 0.00543 | 0.0185 | 0.0449 | 0.00545 | 0.314 | 0.00186 | 0.00139 |
217-5a | 0.905 | 0.00669 | 0.0797 | 0.0216 | 0.00585 | 0.0658 | 0.00986 | 0.342 | 0.00157 | 0.00111 |
217-5b | 0.925 | 0.00576 | 0.061 | 0.018 | 0.00513 | 0.0656 | 0.0094 | 0.287 | 0.00187 | 0.00125 |
217-6a | 0.844 | 0.00645 | 0.0675 | 0.0197 | 0.0737 | 0.0316 | 0.0147 | 0.297 | 0.00154 | 0.00125 |
217-6b | 0.284 | 0.00623 | 0.666 | 0.00623 | 0.0384 | 0.024 | 0.0117 | 0.15 | 0.00146 | 0.00111 |
217-7a | 0.343 | 0.00548 | 0.574 | 0.00548 | 0.0717 | 0.023 | 0.0107 | 0.32 | 0.00152 | 0.00139 |
217-7b | 0.846 | 0.00507 | 0.127 | 0.0144 | 0.0131 | 0.0479 | 0.0133 | 0.311 | 0.00151 | 0.00139 |
217-8a | 0.496 | 0.00722 | 0.439 | 0.00722 | 0.0521 | 0.0325 | 0.0128 | 0.382 | 0.00179 | 0.00111 |
217-8b | 0.512 | 0.00703 | 0.41 | 0.00703 | 0.0639 | 0.0272 | 0.0139 | 0.232 | 0.00173 | 0.00125 |
217-1 | 0.0136 | 0.00346 | 0.956 | 0.00346 | 0.0271 | 0.0233 | 0.00359 | 1.98 | 0.00159 | 0.00111 |
217-2 | 0.978 | 0.00352 | 0.014 | 0.0261 | 0.00614 | 0.042 | 0.00194 | 0.686 | 0.0016 | 0.00125 |
217-3 | 0.932 | 0.00355 | 0.0336 | 0.00355 | 0.0292 | 0.0324 | 0.00491 | 0.279 | 0.00174 | 0.00125 |
217-4 | 0.658 | 0.00135 | 0.32 | 0.00555 | 0.0174 | 0.0268 | 0.00424 | 0.473 | 0.00171 | 0.00111 |
353-3a | 0.554 | 0.00704 | 0.36 | 0.00704 | 0.0699 | 0.0305 | 0.0163 | 0.344 | 0.0017 | 0.00125 |
353-3b | 0.219 | 0.00268 | 0.671 | 0.00695 | 0.0977 | 0.0238 | 0.0119 | 0.289 | 0.00157 | 0.00111 |
353-4a | 0.768 | 0.00473 | 0.198 | 0.00993 | 0.0283 | 0.0505 | 0.00628 | 0.536 | 0.00181 | 0.00125 |
353-4b | 0.684 | 0.00454 | 0.224 | 0.0108 | 0.0774 | 0.08 | 0.0149 | 0.267 | 0.00166 | 0.00111 |
353-5a | 0.767 | 0.00596 | 0.159 | 0.0124 | 0.0628 | 0.0303 | 0.0109 | 0.357 | 0.00156 | 0.00111 |
353-5b | 0.832 | 0.00619 | 0.126 | 0.0111 | 0.0324 | 0.035 | 0.0096 | 0.397 | 0.00166 | 0.00111 |
353-6a | 0.0487 | 0.00176 | 0.855 | 0.006 | 0.0856 | 0.0216 | 0.0105 | 0.222 | 0.00199 | 0.00125 |
353-6b | 0.829 | 0.00561 | 0.127 | 0.00561 | 0.0373 | 0.0252 | 0.00696 | 0.36 | 0.00228 | 0.00111 |
353-1 | 0.41 | 0.000743 | 0.502 | 0.00422 | 0.0811 | 0.0177 | 0.0063 | 0.329 | 0.00132 | 0.00097 |
353-2 | 0.747 | 0.00309 | 0.225 | 0.00726 | 0.0252 | 0.0447 | 0.00267 | 0.513 | 0.00154 | 0.00097 |
353-7 | 0.448 | 0.0009 | 0.537 | 0.0041 | 0.0122 | 0.0273 | 0.00346 | 0.433 | 0.00178 | 0.00125 |
353-8 | 0.718 | 0.00223 | 0.261 | 0.00608 | 0.0165 | 0.038 | 0.00408 | 0.268 | 0.00177 | 0.00111 |
545-1 | 0.991 | 0.00293 | 0.00743 | 0.026 | 0.00139 | 2.6 | 0 | 0 | 0.00216 | 0.00111 |
545-2 | 0.985 | 0.00277 | 0.0128 | 0.024 | 0.00246 | 2.8 | 0 | 0 | 0.00187 | 0.00097 |
545-4 | 0.972 | 0.003 | 0.0277 | 0.025 | 0.000777 | 2.5 | 0 | 0 | 0.00222 | 0.00111 |
857-1 | 0.974 | 0.00338 | 0.0229 | 0.025 | 0.00349 | 2.2 | 0 | 0 | 0.00176 | 0.00111 |
857-2 | 0.84 | 0.00148 | 0.158 | 0.00656 | 0.00249 | 3.2 | 0 | 0 | 0.0022 | 0.00125 |
857-3 | 0.36 | 4.22e-05 | 0.627 | 0.0024 | 0.0111 | 0.017 | 0.002 | 1.9 | 0.00152 | 0.00126 |
857-4 | 0.278 | 0.0004 | 0.719 | 0.00392 | 0.00162 | 0.09 | 0.00152 | 0.8 | 0.00149 | 0.000558 |
Readout Electronic Unit
analog to digital converter
Data Processing Unit
Calibration and Performance Verification
(Planck) High Frequency Instrument