Archive for the ‘Design Tools’ Category

Cadence: VCO Design Using SpectreRF

Tuesday, September 1st, 2015

I was looking for a way I could plot the output frequency of a ring oscillator versus an input tuning voltage.   I did not find anything easy and fast in the literature but I think PSS is the key for the more formal methods.  PSS = Periodic Steady State.  I will look at this later most likely for other applications.  To see what I did do for a useful plot of F versus Vtuning see below.

Research Links





The current consumption of the ring oscillator is more or less proportional to frequency and thus can be used as a plot of frequency versus voltage.  The tuning voltage goes into a gate of an mosfet.  You can see most of the tuning action occurs just below the Vt of that mosfet since the fet is being used with such low currents.

Data Points

  • 500 kHz @ 69 nAmp
  • 200 kHz @ 31 nAmp

Assuming current consumption directly proportional to frequency gives 0.000014 nAmp / Hertz.  This checks out.


1 nanoamp Current Source with No Resistors Using Self Cascode MOSFET

Thursday, August 13th, 2015

Note the 500M Ohm resistor is only to test the current reference.  It would be replaced by your application circuit.

Research Links

 Archive:  Current-Source.7z     Program = LTSPICE

Extract into directory.  Includes the required MOSFET library file.



Output Current


Supply Current

Monte Carlo Analysis with Cadence and the XFAB Design Kit

Wednesday, July 8th, 2015

Getting Monte Carlo analysis to work on Cadence can be a bit of a puzzle given how Cadence is a ball of various software tools stuck together with spit.  You have have seen the following intermodal nastygram:

ADEXL-5052 Monte Carlo run stopped because no statistical data generated for the test

Research Links

Adding Series 4000 CMOS library to LTSPICE

Thursday, June 25th, 2015

Research Links

LTSPICE Phase Lock Loop Behavioral Simulation

Thursday, May 21st, 2015

Behavioral Phase Lock Loop Schematic file

Capacitor Charge Sharing

Friday, April 17th, 2015

When reading about charge pumps you will encounter a phrase like "they act like resistors".  The following example demonstrates why they say that.



So each capacitor ends up with 1/2 Volt on it.  That means the system  starts with 1/2 Joule of energy and when the transfer of charge is done total energy in the system is 1/4 Joule.  

So what happened to the lost 1/4  joule?  It got dissipated in the series resistor.  What about if you do not use a resistor and just charge up C1 and connect it to C2?  

Research Links

Sage: Open Source Mathematics Software System

Thursday, December 25th, 2014

Sage is a free open-source mathematics software system licensed under the GPL. It builds on top of many existing open-source packages: NumPySciPymatplotlibSympyMaximaGAPFLINTR and many more
Access their combined power through a common, Python-based language or directly via interfaces or wrappers. → TourTutorialDocumentation
Mission: Creating a viable free open source alternative to Magma, Maple, Mathematica and Matlab.


Research Links


Using GraphViz to Draw Networks

Friday, December 19th, 2014

This GraphViz graph was animated using vis.js

Research Links


Friday, December 19th, 2014

I want LTSPICE or otherwise to put out a spice deck like netlist as shown in the photo inset and the video embedded below. 

 I have not yet found a way to get this type of output.  All the output formats you can select for export in LTSPICE have the form:


RefDes1.Pin1, RefDes2.Pin1 …….



Which of course is suited to pcb layout programs but not what I am trying to do.   See ExpressPCB Netlist format.

Research Links

LTSPICE: Dual Modulus 8 9 Current Mode Prescaler Files – Complete Set with IBM 65nM Files Adapted from MOSIS

Monday, December 15th, 2014


LTSPICE: 8/9 Current Mode Prescaler Files – Complete Set with IBM 65nM Files Adapted from MOSIS