![]() ARP, EMS, sum the CVs into the tempco resistor through different value resistors. In both cases TCs of 30 ppm are lower than needed, but as they vary +/-10% some rated at 3300 ppm will be correct for case 1. If R2 is a 1k 3600ppm tempco then R1 needs to be 13.6k. If R1 is the larger resistor with negligible TC and R2 the tempco the composite TC is given by: In this case the TC is changed by being in a potential divider with a resistor having a much smaller TC and will be reduced so a larger TC is needed. In this case the TC should be exactly the same as the transistor: 3353ppm 25 deg C.Ģ) put the tempco resistor at the transistor base and the trimmer in the adder feedback. There are two ways of summing and compensating:ġ) put the tempco resistor in the adder feedback to reduce the 1V/oct by a factor of 50 to 20mV/oct and have a trimmer to get 18.5mV/oct at the transistor base and take up prior errors. Ignoring that "feature", in the last schematic one of VR1 and VR2 is redundant, they both adjust the scale. They are also sensitive to magnetic fields. ![]() UJTs are temperature sensitive devices so compensating an exponential converter won't help a lot as the oscillator still won't be stable.
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