Theo Verelst Synth Related Subjects page
Some circuits and ideas fit in the synthesizer area, but may
equally well be applied elsewhere.
The ideas on using a curve lenght feedback or a PLL framed loop
based exponential conversion and derived sets of 2pow(1/n) voltages
and related simulataneous (cheap) multiple multiplying da/ad
convertion units are my own, and are not known to me from literature,
although it is perfectly possible they exist without my knowledge.
I consider them worth implementing and engineering and researching
a bit furhter on, a voltage based exponatial converter can be
used both for synth control voltages and lots of other applications
such as analog multiplication (with a exp conv in a feedback for
log conv). Please note that contrary to my other electronics
pages, these ideas are as yet untested, simply because I
currently don't have the facilities.
Repeated Copyright Notice: Evidently presenting these
materials on the net allows you to try and built them for yourself,
but any right to present, publish, or sell the results is
reserved. Contact me.
Offset Compensation
In a dynamical system, opamp's offset voltage my be compensated for,
by measuring the current (output) offset, and applying a
proportional voltage with the right polarity to one of its
inputs.
A time locked voltage based exponential decay circuit idea
Offset compensated
|--------------------|
|Hi-Zin |
| |\ |-------| |
Vref >---------------------------------|-| >-----| |----->
| | | | | | |/ |-------| |
| | | | | |Buffer | S&H |
| --- | | | | | |------------|-------|
| --- | | Rd | | 10Rd | |
| | Ce | | | | | |
| | | | | |----------
| | --| --| | |
| | |--o |--o | |
| | --| | --| | | |
| | | | | | | |
| -----------|------ | | |
| | | | | |
| --- | ---------|---|-----|
| | | | |
| -----------|-|--------|---|---------------------
| | |-----------| / \ | |
| | | Sequencer | /+ -\ | Comp |
| | |-----------| /-----\| |
| | | | | | |
| | |-----------| | | | |
| | |Clock /\/\|-----| |------------------- |
| | |-----------| | |\ |----| | |
| | | |-|+\ | | | |
| | |-----------| | >--|S&H |--| |
------| V/2 (RC) |------------|-/ | | |
| |-----------| |/ |----| |
------------------------------------------------
(switched) (instrumentation)
Use a dynamically mirrorred version for disturbance compensation,
by switching the capacitor upside down dynamically.
Outine time diagram:
| ----\
| / -
| / \
| / --
| / \
| / ---- /
| | \ |
| | ---------- |
|===/-------------------------------\===/
|<-------->|<------------------>|<->|
Tcharge Tdecay Tvar
|<--------------------------------->|
Tperiod
Application: multiplying da converter
Use the progression of voltages and a switchable integrator
to (MSB first) contstrue an n bit word based analog voltage.
The reference voltage acts as the voltage multiply input,
with the zero point adjusted exactly at ground level.
S&H for multiple outs of course, in various ways.
A PLL based alternative for accurate lin-log convertion
The switched (small scale) variated ramp is made variable through
frequency based fitting.
Combination with integrating sample and holds for
multichannel AD
Only an intgrator and comparator per channel.