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Moved the ECNs from atrf/ecn to the top-level.
This commit is contained in:
Werner Almesberger
@@ -1,6 +0,0 @@
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Number Status Description
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------ ------- ---------------------------------------------------------------
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0001 Edit Adjust balun component values
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0002 Done Add load capacitors to 16 MHz crystal
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0003 Edit Replace balun and filter with integrated balun
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0004 Edit Take into account layout considerations for RF
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@@ -1,16 +0,0 @@
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Adjust balun component values
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Some of the components specified in the schematics were not at hand
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in my lab and were thus replaced with similar parts. Furthermore, the
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LED color was changed to ease visual identification:
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Component Norminal Board 1 Board 2
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--------------- --------------- --------------- -------------------
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LED (D1) red red red-orange
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C6/C7 0.82 pF 0.7 pF 0.9 pF
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L2/L3 4.3 nH 4.7 nH 4.7 nH
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The resulting spectrum should be examined to determine which variant
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performs better. Note that the discrete balun circuit shall be
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replaced with an integrated balun later on.
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@@ -1,48 +0,0 @@
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Add load capacitors to 16 MHz crystal (C14, C15)
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The crystal has a specified load capacitance of 8 pF. The AT86RF230 has
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an internal capacitor array that can be trimmed in 16 steps from 0 pF to
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4.5 pF.
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The crystal has a nominal tolerance of 15 ppm at 25 C plus a temperature
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tolerance of 15 ppm. The following deviations from 1 MHz at CLKM were
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measured with the CNTR board, roughly at 20-25 C:
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Board Error Meas. accuracy C14/C15 Trim
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(f, ppm) (ppm, nom.) (pF) (pF)
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--------------- --------------- --------------- ------------ --------
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2, "orange" +268 99.6 NC 0
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+266 99.5 NC 0
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+266 40.0 NC 0
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+148 99.8 NC 3.0
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+147 99.7 NC 3.0
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+147 40.0 NC 3.0
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+111 100.0 NC 4.5
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+110 99.8 NC 4.5
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- 13 99.9 15 0
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- 14 100.0 15 0
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+ 11 99.9 12 0
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+ 11 99.6 12 0
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(cleanup) + 14 100.0 12 0
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+ 14 100.0 12 0
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1, "red" +263 99.7 NC 0
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+263 100.0 NC 0
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+107 99.3 NC 4.5
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+108 100.0 NC 4.5
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+ 24 99.8 10 0
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+ 24 100.0 10 0
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- 9 99.7 10 4.5
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- 9 100.0 10 4.5
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(cleanup) + 14 100.0 12 0
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+ 14 100.0 12 0
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(Multiple measurements to assess CNTR performance and drift. Note that
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CNTR measurements are repeatable within 1 ppm, so the nominal accuracy
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appears to be far too pessimistic.)
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Conclusion: these measurements suggest that, combined with parasitic
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capacitance, load capacitors of 12 pF make the crystal roughly half the
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trim range faster than 16 MHz.
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@@ -1,58 +0,0 @@
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Replace balun and filter with integrated balun
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We consider the balun needs for the AT86RF230 and the TI/Chipcon
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CC2520 we may try as a design alternative.
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For the AT86RF230, Atmel recommend baluns with integrated filter,
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namely the Wuerth 748421245 and the Johanson 2450FB15L0001, both in the
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AR86RF230 data sheet.
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For the CC2520, TI recommend a microstrip-based design for the balun,
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both in the CC2420/CC243x/CC2480 application note [1] and the reference
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design [2], without fully characterizing neither the transceiver's RF
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output nor all the components in the balun.
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Johanson lists the 2450FB15L0001 [3] and even a 2450BM15B0002 [3] for
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the TI/Chipcon CC2520, but not even Octoparts is able to find a
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distributor for these parts.
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Digging deeper, TI reveal more information about the balun in [5].
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Finally, TI somewhat hesitatingly acknowledge that the Murata balun
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LDB182G4510C-110 can be used for the CC2520 [6], with a 3.9 nH inductor
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connecting RF_P and RF_N, the balun coupled to GND not directly but via
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10 nF, and finally an LC low-pass filter with 1.5 nH and 2.2 pF at the
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output, for EMI compliance.
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Note that this also means that CC2520 and AT86RF230 both have an
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impedance of 100 Ohm.
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A balun without filter similar to the Murata part would be the Johanson
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2450BL15K100.
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Manufacturer Part number Package Digi-Key Price/Qty
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--------------- ----------------------- ------- --------------- ---------------
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Wuerth 748421245 0805-6 732-2230-1-ND 2.15/25
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732-2230-2-ND 0.753/4000
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Johanson 2450FB15L0001 0805-6 - -
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Johanson 2450BM15B0002 0805-6 - -
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Johanson 2450BL15K100 0805-6 712-1045-1-ND 0.488/10
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712-1045-2-ND 0.225/4000
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Murata LDB182G4510C-110 0603-6 490-5023-1-ND 0.325/10
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490-5023-2-ND 0.114/4000
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[1] http://www.ti.com/litv/pdf/swra098d
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[2] http://focus.ti.com/docs/toolsw/folders/print/cc2520em_refdes.html
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[3] http://www.johansontechnology.com/images/stories/ip/baluns/Balun_Filter_Combo_Matched_2450FB15L0001_v11.pdf
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[4] http://www.johansontechnology.com/images/stories/ip/baluns/balun_filter_combo_matched_2450bm15b0002_v2.pdf
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[5] http://www.ti.com/litv/pdf/swra236a
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[6] http://e2e.ti.com/support/low_power_rf/f/155/t/15910.aspx
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Conclusion: the Wurth balun appears to be the safest choice for
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prototyping the AT86RF230. Due to its high cost, a circuit with a
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discrete filter may be considered for larger quantities.
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For the CC2520, it's probably safest to directly try the Muarta balun
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with the recommended discrete filtering circuit.
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@@ -1,73 +0,0 @@
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Take into account layout considerations for RF
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There are a number of layout considerationg when designing RF systems
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that were not taken into account or not quantified when making the
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first design.
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- transmission line width
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The microstrip [1] transmission line connecting the balun and filter
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circuit with the antenna must be impedance-matched with the antenna.
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The rule of thumb according to [2] is to make its width twice the
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board thickness, in this case 0.8 mm or 31.5 mil.
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The microstrip calculator at [3] also takes into account the
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thickness of the copper, 1 oz, and yields a slightly narrower 57.5
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mil or 1.46 mm.
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A more elaborate calculator can be found at [4].
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- via spacing
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Section 4.2 of [5] recommends a via spacing of no more than
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Lvia = C/sqrt(Er)/Fres
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where
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C = the speed of light, 3*10^8 m/s
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Er = the board's dielectric constant, 4.5 for FR-4
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Fres = the resonance frequency, at least 24.5 GHz
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We thus obtain Lvia = 5 mm.
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- component placing
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[5] places DC blocking, balun, and filter close to the transceiver,
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with only the feed line between the RF circuit and the antenna. Thus,
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no changes are needed.
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- feed line termination
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Point 12 of [6] warns us that we may need to terminate the
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transmission line if it is longer than 20% of the signal's rise time.
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Point 1 of [6] gives the rise time as 1/(10*Fclk), which looks as if
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it's meant for digital signals. But we'll use it anyway.
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[2] gives us the typical propagation delay for a microstrip as
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150 pS/in.
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This means that Lmax = 0.2*tr*v
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with
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tr = 1/24.5 GHz
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v = 1 in/150 pS
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We thus obtain Lmax = 1.4 mm
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[2] suggests that the maximum unterminated stub is L(in) = tr(nS).
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With tr = 1/(10*Fclk), we thus obtain Lmax = 1.04 mm.
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Not sure if all this even applies to antennas. This needs looking to by
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someone who understands about RF.
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[1] http://en.wikipedia.org/wiki/Microstrip
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[2] http://www.hottconsultants.com/techtips/rulesofthumb.html
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[3] http://www.cepdinc.com/calculators/microstrip.htm
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[4] http://mcalc.sourceforge.net/
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[5] http://www.ti.com/litv/pdf/swra236a
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[6] http://www.pcbmotif.com/home/index.php?option=com_content&view=article&id=104&Itemid=137
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Conclusion: the antenna feed line needs to be revised. The via spacing
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of the RF area needs to be examined. The recommended spacing may be
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beyond the capabilities of a DIY process, though.
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