net positive regeneration around the loop that includes r5 if resistor r8 were replaced with a capacitor the gm cell current mirror and output stage would function in a manner similar to a classic operational amplifier and an external feed back path outer control loop would then be required to control the oscillator amplitude however by placing the resistor r8 in the inner control loop the present invention provides a simple and accurate control circuit without the delays associated with operational amplifiers which behave as integrators the voltage swing at the output can be well controlled by the choice of tail current for the gm cell and the value of r8 in a practical implementation a tuning circuit typically including a varactor diode and resistive matrix for interfacing to an automatic frequency control signal would also be coupled to the crystal such a tuning circuit is disclosed in co pending u s patent application ser no 09 032 436 filed feb 27 1998 entitled 34 cubic type temperature function generator with adjustable parameters 34 which is herein incorporated by reference to adjust the center voltage of the output voltage v out an additional current can be forced into r8 one way to accomplish this is to connect a current source between the base of q10 and gnd another technique is to force an additional current into the collector of.