1. Philippe Picard1 System Design 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Aperture Arrays system design Front end RF combining: an efficient way to reduce DC power requirements? Philippe Picard Station de radioastronomie de Nançay Philippe.Picard@obs-nancay.fr Stephane Bosse Station de Radioastronome de Nançay Stephane.Bosse@obs-nancay.fr Severin Barth Station de Radioastronomie de Nançay Severin.Barth@obs-nancay.fr

2. Philippe Picard2 System Design 4 th SKADS Workshop, Lisbon, 2-3 October 2008 An all digital system can be viewed as power hungry system  the most flexible system  « max. instantaneous FoV » ~ antenna element FoV  calibration parameters apply to the antenna element level A system with front end RF combining can be viewed as a way to reduce power  « max. instantaneous FoV » reduced by the combining factor  not so easy to calibrate compared to an all digital system DC power requirement is a driving parameter for yearly recurrent operating cost and could be very high for AA systems with millions of antenna elements and associated digital processing Need of ultra low power design wherever it can apply About DC power parameter

3. Philippe Picard3 System Design 4 th SKADS Workshop, Lisbon, 2-3 October 2008 LNA Tile analogue conditioning, Transport interface LNA Tile analogue conditioning, Transport interface Analogue conditioning ADC Analogue conditioning ADC LNA Tile analogue conditioning, Transport interface LNA Tile analogue conditionning, Transport interface Analogue conditioning ADC Analogue conditionning ADC LNA Tile analogue conditioning, Transport interface LNA Tile analogue conditioning, Transport interface Analogue conditioning ADC Analogue conditioning ADC Signal transport pol 1 Signal transport pol 2 Signal transport pol 1 Signal transport pol 2 Signal transport pol 1 Signal transport pol 2 2 pol antenna elements Tile level Station digital processing AA all digital system: generic design P dig = P1 + P2 + P3 P1 P2 P3=P SDP /N P anc P lna

4. Philippe Picard4 System Design 4 th SKADS Workshop, Lisbon, 2-3 October 2008 LNA Phase shif,t Amplitude shift  Phase shift, Amplitude shift Phase shift, Amplitude shift Tile analogue conditioning, Transport interface, Comand and control interface LNA Phase shift, Amplitude shift  Phase shift, Amplitude shift Phase shift, Amplitude shift Tile analogue conditioning, Transport interface, Comand and control interface Tile level beamformer chip pol 1 beamformer chip pol 2 16 → 1 16 x 2 pol antenna elements Analogue conditioning ADC Pol. 1 Analogue conditioning ADC Pol. 2 Station digital processing AA with RF combining: generic design P bfc P anc P int P dig P lna

5. Philippe Picard5 System Design 4 th SKADS Workshop, Lisbon, 2-3 October 2008 P lna = DC power (LNA) P anc = DC power (tile analog contitioning + transport interface) P dig = DC power ( ADC analog conditionning + ADC + station processing 1 pol.) P bfc = DC power for 1 input of beamformer chip P int = DC power for command and control interface comb = combining factor nbeam = number of RF beams P ref = (P lna +P anc )/DC effan + P dig /DC effdig P eqc = P lna /DC effan + (P bfc /DC effan ).nbeam + ((P anc /DC effan )+(P dig +P int ) /DC effdig ) / comb).nbeam For a system with N antennas per station, 2 pol., S stations: DC power (all digital) = 2.N.S.P ref. DC power (RF combining) = 2.N.S.P ref.power_ratio P ref = reference total power for 1 polarization, all digital design P eqc = power for 1 polarization with RF combining + digital processing DC effan = analogue power supply efficiency (0.6) DC effdig = digital power supply efficiency (0.72) power_ratio = P eqc / P ref plot versus P dig N=75000 antennas S=250 stations 2 pol.

6. Philippe Picard6 System Design 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Parameter weights in the power_ratio: Today digital ASICs,FPGA and CPUs in 90nm and 65nm silicon process Emerging ASICs, FPGA and CPUs in 45nm and 32nm process Power saving

7. Philippe Picard7 System Design 4 th SKADS Workshop, Lisbon, 2-3 October 2008

8. Philippe Picard8 System Design 4 th SKADS Workshop, Lisbon, 2-3 October 2008 For the same total instantaneous FoV options are:  to combine a small number snb of elements in one RF beam  to combine k.snb elements in k separate RF beams For DC power efficiency, it’s better to combine a small number of elements in one RF beam RF beams: multibeaming or not?

9. Philippe Picard9 System Design 4 th SKADS Workshop, Lisbon, 2-3 October 2008 Be aware, it’s only a tool… With clever input parameters it’s easy to show what we want to show… Only a deep documented analysis of the power budget for a specific design can deliver accurate input parameters…

10. Philippe Picard10 System Design 4 th SKADS Workshop, Lisbon, 2-3 October 2008 An all digital AA design gives the most flexible system and easiest to use, but if MW are not for free, RF combining can reduce DC power (with reduced instantaneous RF FoV and calibration to be considered) => Need to be able to test the two systems in the next AA developpment phases  Design front end with optional RF combiners (as front end « plug ins »?)  Design station digital processing being able to optionally accept RF combined antennas at inputs  Continue to work on RF combiners with the newest Si process To do next:

11. Philippe Picard11 System Design 4 th SKADS Workshop, Lisbon, 2-3 October 2008 The end Thank you