Designed by SM6MUY, Bengt and SM6PGP, Hannes
VCXO with PLL to be locked to any kind of frequeny reference. The first version was built approx 1995. Now several modification have been done. The latest was to remove the eeprom and some HC-logic and to replace it with a PIC 16C84/16F84 that can be programmed on board.
The heart of the design is an emitter coupled harmonic oscillator( BFS520) which have good short term stability. (RF design, Oscillator design handbook) It is easy to add a varactor in this circuit to pull the oscillator an small amount in frequency. The oscillator is followed by a transistor buffer (BFS520). The signal is fed into an attenuator and a small Si MMIC (MSA2111) to further increase isolation towards the oscillator. In some cases I have used the MMIC as a multipler. Then the attenuator is adjusted to make the MMIC go into compression it is followed by a helixfilter(TOKO) to select the wanted harmonic. The resistor in the bias circuit can be optimized to improve conversion loss in the multiplier.
The synthesizer is a Siemens/Infineon PMB2306T wich is loaded with
data, Data-Enable-Clock. The signals for loading the synt is generated
by the PIC processor 16C84/16F84. The PIC can be programmed on board
by removing two 0ohm jumpers. I use MPLAB from Microchip and a
attached to the PC parallell port. I will add some examples of code for
the PIC processor on this page later.
Programming software: look for PICPROG by Conquest systems (ZL1HIT) a very nice pice of software and a good description of the needed hardwar, or IC-PROG (added 2004-10-26)..
Some possible combinations of oscillator and reference frequencies:
OSC FQ REF FQ N-div R-div(13 MHz) R-div(10 MHz) R-div(5MHz)
90.666666 MHz 333.333
(2320 MHz xverter)
96.000000 MHz 500 kHz 192 26 20 10 (1296 MHz xverter)
106.50000 MHz 500 kHz 213 26 20 10 (10368 MHz xverter)
108.06666 MHz 66.6666 kHz 1621 195 150 75 (SK6MHI 1296.800 MHz)
117.00000 MHz 500 kHz 234 26 20 10 (5760 MHz xverter)
125.50000 MHz 500 kHz 251 26 20 10 (24192 MHz xverter)
128.00000 MHz 500 kHz 256 26 20 10 (1296 MHz xverter)
The PLL loop filter has to be designed for the selected reference
There is no component values in the component placing drawing.
Use PLL loop filter design by National Semiconductor. I have used a 3:rd order filter. Kvco has to be measured (typical 1-2 kHz/V). Loop BW has to be selected (10 -100 Hz gives reasonable component values)
An example of a loopfilter :
fosc = 90.666666
C1 = 33nF
fref = 333.333333 kHz C2 = 330 nF
Ndiv = 272 R2 = 56 k
Rdiv = 15 (5 MHz reference osc) R3 = 120 k
Kvco = 1 kHz/V C3 = 120 pF
Icp = 1 mA
Att = 60 dB
Phase marg = 56 deg
loop BW = 30 Hz
The VCXO/PLL can be built in a standard 55 x 72 mm tinplate
VCXO Phase noise measurement
A phase noise measurment has been performed with the new
AGILENT E5052 Signal Source Analyzer. I got this
opportunity at an Agilent instrument demonstration.
Thanks to the Agilent guys !
Things, good to know if you are trying to build this VCXO.
The xtall has to be approx 3 - 4 kHz higher in frequency than the
fq. So if you plan building it for 106.5 MHz then you have to order an
xtall for 106.503 MHz, this is because the wanted pulling range is +/-
3 kHz. I do usually order 5:th overtone series resonant xtalls.
Run the oscillator and connect a trimpot to gnd and +5 V) and the wiper to the cap-diode so you can check that the osc is running ok and that you get the wanted pulling range. Tune the trimcaps in the osc so that you get approx 2.5 V when you are at the centerfq and so that the oscillator starts at power on. The inductor and the type of capdiode affect the pulling range, you may have to change these. The inductor usually ends up in the range 100-390 nH.
In some cases it has been necessary to remove the 2.2 pF cap mounted from base of the osc transistor to ground.
Change from rev F to rev G, I found that there was a capacitor (1 nF) lost at the bias of MSA2111 between the inductor and the resistor. Should be connected from the connecting point of the 39 ohm/220nH and to gnd.
Unfortunately I have found out that the
is becomming obsolete !
I have no plans in modifying the vcxo circuit to accomodate a new synthezeiser. 2001-04-13
Schematic in pdf or in postscript format:
schematic in pdf (35k)
schematic in encapsulated postscript (64k)
PCB layout in pdf or in postscript format:
Board layout in pdf (30k)
Board layout in encapsulated postscript (124k)
Component placement in pdf or in postscript format:
Component placement in pdf (21k)
Component placement in encapsulated postscript (38k)
Use GSview to view postscript documents or download and print on a postscript printer.
PIC asm and hex code examples (16C84), the code is as it is and i
not put much effort in the programming
as I am no programmer and just do it because I have to.
Anyone who likes to create better code may do so and I am interested in a copy.
106.5 MHz (LO for 10 GHz xverter)
ref = 500 kHz
125.111111.... MHz (LO for P3D 23/13 cm up/dwn link)
ref = 111.111 111...kHz
Info for creating the databytes
Refer to datasheet for the PMB2306
this page may only be used for personal use, for any other use pse contact (s m
6 p g p ( a t ) i l l i p e . s e)
Changed 2014-07-26 by SM6PGP