In portable battery operated products such as a selective call receiver, it is sometimes necessary to use active components requiring voltages higher than produced by a single conventional battery such as a AA, AAA, watch cell, or the like. Volumetric size constraints in present state of the art selective call receivers dictate that additional batteries cannot be accommodated. Hence, designers have opted instead to use a conventional voltage multiplier to supply the higher voltages. The use of voltage multipliers brought about other problems such as their voltage variation versus temperature and the finite time necessary stabilize their multiplied output voltage. Accordingly, any voltage sensitive circuitry powered by the multiplier should be kept inactive during the stabilization period or unpredictable operation could occur.
Conventional power-on reset circuitry addressed these problems by sampling the multiplied voltage output and holding voltage sensitive circuitry in an inactive state during the stabilization period. These prior-art power-on reset systems typically comprise a complex analog comparator with hysteresis and a separate temperature compensated precision voltage reference. The comparator operates to compare the precision voltage reference to the magnitude of the multiplied output voltage, and release a reset signal when the multiplied output voltage reaches a value allowing proper operation of the voltage sensitive circuitry. This approach functions acceptably but at a cost of higher current drain and increased circuit complexity in the temperature compensated precision voltage reference, neither of which can be tolerated in present state of the art selective call receiver systems. Moreover, using conventional integrated circuit processing and technology, it is difficult if not impossible to construct a comparator with controllable hysteresis that operates effectively from a single power cell having a nominal voltage of substantially 1.0 volts DC. Many attempts have been made to overcome this problem, but none has been successful.
Thus, what is needed is an intrinsically temperature compensated voltage detector capable of providing a power-on reset signal denoting when the multiplied output voltage reaches a value allowing proper operation of the voltage sensitive circuitry.
USPTO Backgrounds
USPTO Backgrounds