Alan Stummer
Research Lab Technologist


Variable Gain RF Amplifier

I am curious who uses what.  Are these webpages a waste of time, or are they any help to others?  Are the circuits, software and utilities appearing in other labs?  Please send your comments or suggestions or what you have used (or not) or schematics of your version or pictures or anything!   Email me, or be creative and send a postcard! I want to hear from the vacuum! Links

NOTICE: This webpage and associated files are 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.


Started September 2012 for Dylan Jervis in Joseph's lab.  The amplitude of an RF input signal is linearly adjusted from zero to unity by an amplitude control input signal.  The amplitude control is ±10V, where -10V is 0% output, 0V is gain of 0.5 and +10V is gain of 1.  The heart of the unit is Texas Instruments' VCA822 on an eval board.  TI conveniently provides these blank eval boards for a nominal fee.  The maximum output is at least 1.25Vrms or +15dBm.  Small signal frequency is up to 150MHz (for -3dB), large signal is 120MHz.

The circuit is quite simple:  RF input goes to the VCA822, as does the gain control voltage, the VCA822 output is the unit's output.  The bipolar ±5V supply is provided by a single DC supply and a pair of zeners.  The whole assembly mounts in a metal box on bulkhead SMA connectors.

WARNING!  L1-2 and C1-2 are marked backwards on the board (you get what you pay for).  The markings "Vs+" and "Vs-" are correct.  Double check tantalum polarities before installing them.

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