Described is an apparatus of a thermal sensor and/or bandgap reference circuit which is independent of an operational amplifier. The apparatus comprises: a forward biased diode circuit having one or more diodes; a first switch-capacitor sampler coupled to the forward biased diode circuit, the first switch-capacitor sampler to provide a reference voltage which is proportional to absolute temperature; and a second switch-capacitor sampler coupled to the forward biased diode circuit.