[time-nuts] Oscillatek 2352

[Charles Steinmetz]

ed wrote:

> I'd recommend against offsetting the device ground   *   *   *

> In actual application, you should go ahead and provide the +/-
> tune voltage range. It's a little more complicated since you'll need a
> negative supply or offset   *   *   *

> It's fairly easy to make quiet, low current negative supplies from the
> +12 V, if no other ready source is available from the system.

The dawning of the low voltage, rail-to-rail opamp age has created a new 
class of low-power, inverting switching ICs with integrated, low-voltage 
negative regulators.  These are designed to offset the opamp's negative 
supply rail below ground so that RRO opamps can truly pull their outputs 
all the way to ground, not just within millivolts.  Two good examples 
are the LM7705 ("low noise negative bias generator") and the LTC1550, 
but the list is expanding every quarter.

Note that these inverters use internal oscillators at frequencies much 
lower than 10MHz, so there is a possibility of mixing and beating as Ed 
noted.  Also, anyone going this way should make sure the regulator 
output is sufficient to handle the oscillator's needs under all conditions.

Best regards,

Charles