VCO in AN-299

[Ian Fritz]

Jorgen --

It *does* use a heater. Q3 is the heater, Q6 is a clamp, Q4 is the
sensor and A2 is the servo amp. This is explained on p. 2 of the
article.

  Ian

jorgen.bergfors at idg.se wrote:
> 
> Has anybody tried the VCO in National Semiconductor's Application Note 299,
> figure 1? It is a 1 V/oct VCO that is supposed to be virtually free of
> temperature dependence. And it does not use tempco resistors or heaters. It is
> a sipmle circuit with two opamps and one CA3046, that produces a sawtooth
> output. It seems a bit too good to be true. Are there any gotchas? The
> exponential conformity is said to be within 0,25% from 20 Hz to 15 kHz.
> 
> /Jorgen