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Philippe Picard 1System Design4th 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 [email protected]
Stephane Bosse Station de Radioastronome de Nançay [email protected]
Severin Barth Station de Radioastronomie de Nançay [email protected]
Philippe Picard 2System Design4th 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
Philippe Picard 3System Design4th SKADS Workshop, Lisbon, 2-3 October 2008
LNATile analogue conditioning,
Transport interface
LNATile analogue conditioning,
Transport interface
Analogueconditioning
ADC
Analogueconditioning
ADC
LNATile analogue conditioning,
Transport interface
LNATile analogue conditionning,
Transport interface
Analogueconditioning
ADC
Analogueconditionning
ADC
LNATile analogue conditioning,
Transport interface
LNATile analogue conditioning,
Transport interface
Analogueconditioning
ADC
Analogueconditioning
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 antennaelements
Tile level
Sta
tion
digi
tal p
roce
ssin
g
AA all digital system: generic design
Pdig = P1 + P2 + P3
P1 P2
P3=PSDP/NPancPlna
Philippe Picard 4System Design4th SKADS Workshop, Lisbon, 2-3 October 2008
LNA
LNA
LNA
Phase shif,tAmplitude shift
Phase shift,
Amplitude shift
Phase shift,Amplitude shift
Tile analogueconditioning,
Transportinterface,
Comand andcontrol interface
LNA
LNA
LNA
Phase shift,Amplitude shift
Phase shift,
Amplitude shift
Phase shift,Amplitude shift
Tile analogueconditioning,
Transportinterface,
Comand andcontrol interface
Tile level
beamformer chip pol 1
beamformer chip pol 2
16 → 1
16 → 1
16 x2 pol antenna
elements
Analogueconditioning
ADC
Pol. 1
Analogueconditioning
ADC
Pol. 2
Sta
tion
digi
tal p
roce
ssin
g
AA with RF combining: generic designPbfc
Panc
Pint
PdigPlna
Philippe Picard 5System Design4th SKADS Workshop, Lisbon, 2-3 October 2008
Plna = DC power (LNA)
Panc = DC power (tile analog contitioning + transport interface)
Pdig = DC power ( ADC analog conditionning + ADC + station processing 1 pol.)
Pbfc = DC power for 1 input of beamformer chip
Pint = DC power for command and control interface
comb = combining factornbeam = number of RF beams
Pref = (Plna +Panc)/DCeffan + Pdig/DCeffdig
Peqc = Plna/DCeffan + (Pbfc/DCeffan).nbeam + ((Panc/DCeffan)+(Pdig +Pint) /DCeffdig) / comb).nbeam
For a system with N antennas per station, 2 pol., S stations:DC power (all digital) = 2.N.S.Pref.DC power (RF combining) = 2.N.S.Pref.power_ratio
Pref = reference total power for 1 polarization, all digital designPeqc = power for 1 polarization with RF combining + digital processing
DCeffan = analogue power supply efficiency (0.6)DCeffdig = digital power supply efficiency (0.72)
power_ratio = Peqc / Pref plot versus Pdig
N=75000 antennasS=250 stations2 pol.
Philippe Picard 6System Design4th 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
Pow
er
savin
g
Philippe Picard 7System Design4th SKADS Workshop, Lisbon, 2-3 October 2008
Philippe Picard 8System Design4th 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?
Philippe Picard 9System Design4th 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…
Philippe Picard 10System Design4th 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:
Philippe Picard 11System Design4th SKADS Workshop, Lisbon, 2-3 October 2008
The end
Thank you
