Micropower RC oscillator

A micropower RC oscillator comprising;

• a temperature compensating reference voltage means comprising an output terminal resistor and an output terminal transistor which are connected between an output terminal and a ground terminal in series and generating a reference signal having a stable voltage level in view of a temperature variation at the output terminal, wherein the output terminal transistor includes an output stage having a reciprocal voltage down characteristics with the temperature variation, and a PTAT current source, connected to the output stage, having direct proportional characteristics against the temperature variation;
• a voltage amplifying means for amplifying the voltage level of the reference signal generated from the temperature compensating reference voltage means and outputting the reference signal;
• a buffer amplifying means for buffering the reference signal amplified by the voltage amplifying means to output a driving voltage having an increased fan-out capacity;
• an RC oscillation circuit having an RC circuit including a plurality of inverting circuits connected in series and respectively driven by the driving voltage, a variable resistor circuit which forms a closed loop disposed between an output terminal of a head-inverter at an output stage and an input terminal of a tail-inverter, and which changes a resistance value thereof according to an external resistance setting data, and a capacitor disposed between an input terminal of the head-inverter and the input terminal of the tail-inverter and generating an oscillation signal having an oscillation frequency determined by a time constant of the RC circuit at the output stage;
• and
• a level shift circuit for boosting the oscillation signal to a predetermined voltage level and outputting the oscillation signal.

An RC oscillating circuit comprising;

• a plurality of inverters interconnected in series and driven by means of an independently supplied driving voltage;
• and
• an RC circuit including a variable resistor circuit which forms a closed loop between an output terminal of a head-inverter connected to an output stage and an input terminal of a tail-inverter and changes a resistance value according to an external resistance setting data and a capacitor disposed between an input terminal of the head-inverter and the input terminal of the tail-inverter,
• wherein the variable resistor circuit includes a plurality of unit resistors and a resistance regulator for selecting an effective resistance value that contributes to determine an oscillation frequency among the plurality of unit resistors based on the resistance setting data, and wherein each of the plurality of unit resistors includes a p+ diffusion resistor and a polysilicon resistor having opposing characteristics with respect to a temperature variation at a predetermined ratio and generates an oscillation signal having the oscillation frequency determined by a time constant of the RC circuit to the output stage.