FixedSine

Function

This generator provides a pure sine signal with very little drift and phase noise. It sacrifices flexibility for stability, compactness and simplicity.

Options and Alternatives

The generator can be used with any square wave oscillator from the series AQO 7050 by Auris. Refer to the Bürklin catalogue for a list of available frequencies.

The resistors and inductors of the filter have to be adapted to the specific operation frequency. Refer to table 1 for values known to work. The filter design tool hosted at the university of York, UK is recommended to determine reasonable values from scratch.

Filter values known to work for specific frequencies
Freq. R3 L3 C14 L4 C16 R4 type
16.9 MHz 50 Ω 1.5μH 150 pF 2.2 μH 100 pF 300 Ω chebychev

Performance

A generator configured for 20.00 MHz was characterized:

  • frequency drift integrated over a few minutes is less than $1\times 10^{-8}$.
  • frequency drift integrated over approximately one second is less than $1\times 10^{-9}$.
  • according to the manufacturer the jitter of the oscillator is below 1 ps.

Timeline

  • The project was started in July 2015
  • The first prototype was operational in August 2015

Status

About ten devices are in use at Mg.

Developer

Nandan Jha

User

Mg

Principle of Operation

An integrates quartz oscillator provides ​a stable ​square wave signal. A passive four pole LC filter removes the higher harmonics ​to render a near perfect sine waveform. An amplifier is used on output to increase the amplitude and the ability to drive low impedance loads.

Schematic

Layout

Layout (top view)
Layout (bottom view)

Enclosing

Hammond 1590LLBK

Mounting holes of the generator and connectors are compatible with the design of the photodiode amplifier PD-ac-dc.

Test

The oscillator should oscillate right out of the box.

Images

Cost

item amount value total remarks
4-layer PCB 1x 24.50 € 1/4 of 95.43 EUR (Basista-Prototyping)
enclosing 1x 8.20 € Hammond 1590LLBBK
SMA connector 1x 1.60 €
JAE IL-G connector, 3 pin 1x 0.30 €
voltage regulator 2x 0.20 € SOT89
100 µH inductor 2x 0.30 €
10 µF tantalum cap 3x 0.80 €
HF inductor 2x 0.50 € Epcos B82498F
oscillator 1x 2.30 € Auris AQO-7050
opamp AD817 1x 6.55 € fast, high slew rate
resistors, caps, diodes 25x 0.02 € all parts sized 0805
off-cuts 5.00 €
total overall:

When produced as a mini series of 60, the price for the PCB drops to 5.20 € per piece.

Todo

(Icons: :no:: nope, :Ok:: in the works, :ok:: done in the schematic, not yet in layout, :OK:: done)

  1. Add a 1 nF capacitor in parallel to R5. This helps get rid of offset voltages (WTF?)
  2. Use AD817 op-amp due to its fast slew rate. C19 and C21 are not needed for this op-amp.
  3. Opamps aree borderline fast enough --> Better use MMICs in the next version. E.g. ERA-8, or similar.
  4. A polygon on top is not connected to ground.
  5. Ground should be done more properly
  6. Diode D3 is drawn in the wrong direction in the layout