University of Toronto, Physics, Quantum Optics Labs

Alan Stummer, Research Lab Technologist

40K Evaporator DDS Supplies

Includes description and application of the DDS

Power Supplies
Frequency Multipliers and Amps


NOTICE: This webpage and associated files is provided for reference only.  This is not a kit site!  It is a collection of my work here at the University of Toronto in the Physics department. If you are considering using any schematics, designs, or anything else from here then be warned that you had better know something of what you are about to do.  No design is guaranteed in any way, including workable schematic, board layout, HDL code, embedded software, user software, component selection, documentation, webpages, or anything.

All that said, if it says here it works then for me it worked. To make the project work may have involved undocumented additions, changes, deletions, tweaks, tunings, alterations, modifications, adjustments, waving of a wand while wearing a pointy black hat, appeals to electron deities and just plain doing whatever it takes to make the project work.


March '05, Ian Leroux with Alan Stummer for Joseph's lab.  The big picture purpose of this project is to be a precision frequency source around 1.286GHz for evaporative cooling of 40K in the BEC/degenerate fermions experiment.  As a side benefit, it also generates a 983.040000MHz reference for the rest of the lab. The project can be broken into several blocks: power supply, 983MHz source, 321.5MHz et al generation by the DDS, frequency quadrupler and power amplifier.

The power supply is a straight forward linear LDO array, available as a schematic (in native Eagle format) and also as a PDF but which might be out of date.

The core of the project is the power supply for the Analog Device's AD9858 DDS (Direct Digital Synthesis) development board ( schematic) and associated frequency multipliers and amplifiers. A DDS is a digital IC that can generate any frequency up to the reference clock oscillator's Nyquist frequency.  In the AD9858, a clock frequency of 1GHz can generate from 0.233Hz to 400MHz.  The output frequency is set by:
   f o = FW * f sam / 2 32   where f o is the output frequency, FW is the 32-bit frequency word and f sam is the 983.04MHz sample clock frequency.
The desired frequency is mapped out in a LUT (lookup table). On every f sam cycle, the DDS looks in the lookup table for the instantaneous amplitude of f o and sets the output DAC (Digital to Analog Converter) accordingly.  Whereas a 1Hz f o would have 1e9 points defining it, a 400MHz f o would have only 2.5 defining points per cycle.  In the latter high frequency case, a low pass filter set between the fundamental and second harmonic will clean up the output.

The DDS reference clock is generated by the VCO (Voltage Controlled Oscillator) on the development board.  It has been replaced by a 992MHZ VCO from Sirenza (now part of RFMW) capable of running at closer to the maximum 1GHz.  An on-board divider cuts the 983.040000MHz down by 16 to 61.440000MHz.  The VCO is part of an on-board PLL (Phase Lock Loop).  The PLL compares this 61.440000MHz to a very stable reference 61.440000MHz oscillator.  This latter reference oscillator is an OCXO (Oven Controlled Crystal Oscillator).

The 61.440000MHz OCXO is from Vectron. It uses an internal oven to be stable in temperature and time to <30PPB (Part Per Billion, or 1:1E9)/day.  Stability specs include:

Daily aging <±1 PPB
Monthly aging <±20 PPB
Annual aging <±100 PPB
10 year aging <±250PPB

At any given time, the stability depends not only on aging but also ambient temperature, supply and load.  These additional errors can be added to the aging.  The cumulative holdover daily stability becomes  ±30PPB and is split as follows:

Temperature stability (0° to 70°) <±25 PPB
Supply variation (±5%) <±2 PPB
Load variation (0-100%) <±2 PPB
Daily aging <±1 PPB

Because the OCXO is in an environmentally controlled room, the temperature effect is minimized.  The OCXO supply and load too are stable.  This resultant stability allows approaching the 40K ground state transition frequency of about 1.28GHz to within 1KHz with quarterly or semi-annual calibration.  Calibration is to be done against the local Stratum 3 RF sources - A.K.A. FM radio stations - by using the DDS to generate the carrier frequency and then beating against the FM RF carrier.  A 1Hz beat frequency corresponds to 10PPB.

Power Supplies

The only power source is a regulated 9V/1.5A adaptor hard-wired into the DDS box.  The 9V goes through a power switch.  There are four supplies, in the table below.  The three regulated supplies use National Semiconductor's LM1086 family of  LDO (Low Drop-Out) regulators.  Because a large amount of the current goes to the +3.3V DDS core, the power dissipation is equally split between the main +5V and the +3.3V regulators.  Two diodes are used before each +5V regulator to reduce the regulators' power dissipation by lower their input voltage.

Supply Loads Min Typ Max Measured
Raw +9V Cooling fan 175mA 75mA
OCXO 90mA 300mA 120mA, 270mA
Main +5V Development board dividers 175mA
DDS charge pump 105mA
+3.3V regulator <865mA 1.075A
+3.3V DDS 760mA
Stable +5V Development board VCO 15mA

Frequency Multipliers and Amps

The 321.5MHz DDS output is  frequency quadrupled in the RF section.  All components are from Mini-Circuits.  Attenuators are added as required.  The sequence is:

  1. MK-2, frequency doubler
  2. ZX60-2522M, amplifier,19dB gain, 18dBm.
  3. MK-5, frequency doubler
  4. ZASWA-2-50DR, switch (to kill the amplifier input).
  5. ZX73-2500, voltage variable attenuator, 3dB to 40dB.
  6. ZRL-2400LN, power amplifier, 31dB gain, 23dBm.

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