Bruce Griffiths wrote: >> >> > The LTZ1000 datasheet states that 100ppm change in this resistor > produces a 1ppm shift in the LTZ1000 reference voltage. > It is possible to use a 4 terminal resistor for this part to improve > accuracy somewhat as the base current of th compensation resistor is > around 1uA and its emitter current is 100uA. > This isn't ideal but the emitter current is about 40x lower than the > zener current. > On reflection this resistor operates in quasi 3 terminal mode with about 200uA current flowing in one of the sense leads.
> Bruce > > If this resistor is replaced by a modified Howland current source (reference voltage derived from the temperature compensation transistor Vbe) then the 120 ohm resistor can be employed in 4 terminal mode within the Howland circuit. Depending on the degree of elaboration the sensitivity to lead resistance of the 120 ohm resistor can be reduced by a factor of 10-100 or more. Other possibilities include sinking a 4mA current from the zener transistor base node using a current source (with diode clamp to protect the transistor base emitter junction against reverse breakdown) whose value is determined by the 7V reference output of the LTZ1000. However this requires a precision current mirror and a startup circuit. Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
