🚀 go-pugleaf

In article <1992Aug18.140051.10073@donau.et.tudelft.nl> elmar@dutentb.et.tudelft.nl (Elmar van Ginneken) writes:

>What I am looking for is a low power oscillator (<.5 mA @ 5V) running
>at a frequency of roughly 1 MHz.
>However, the frequency-determining component should be an inductor with
>a value of approx. 75 uH. (YES, I'm trying to measure inductance-change..)

	You can make an RL oscillator with a CMOS Schmitt trigger
gate; the time constant is L/R, so your 75 uH inductor will 
require about a 470 ohm resistor.  That would draw too
much current, so try:


+5---------VVVVV--+---VVVVV---GND
                  |
                  +---VVVVV--+
                  |          |
                  -          +----<Lx>----+
                  -          | |\         |
                  |          +-| >O-------+
                 GND           |/

with the two top resistors circa 10k ohms, and the capacitor
1uF (preferably ceramic).  The current from the inverter (a 74HC14
would be best) will come to about 2 mA AC; it would be prudent
to use several inverters in parallel to generate this much
current.  You get six to a package, so:


     |\     |\     |\
-----| >O---| >O-+-| >O--+
     |/     |/   | |/    |
                 |       |
                 | |\    |
                 +-| >O--+
                 | |/    |
                 |       +------
                 | |\    |
                 +-| >O--+
                 | |/    |
                 |       |
                 | |\    |
                 +-| >O--+
                   |/

will be the full 'expansion' of the inverter.

	The problem here is that the current drain will come to nearly
three mA; without using an oscillator that has a lower threshold
voltage than CMOS Schmitt triggers, the inductors you are using
cannot achieve oscillation at these frequencies with the 0.5 mA
current you require.

	So, you will want to raise the resistance, thus lowering
the frequency (to one kHz or so), and use a PLL to generate
a tracking 1MHz signal; this requires three more IC's, a 74HC4046
for the PLL and two MC14520's for the dividers (or perhaps one
4060 or 4020 or 4040 for the divider).

	John Whitmore