Patent ID: 6137324
Filing Date: 2000-10-24
Classification: H03K

Abstract:
A power-on reset circuit for generating a power-on reset pulse that linearly ramps up from a predetermined lower threshold voltage V.sub.cc .degree. to a predetermined upper threshold voltage V.sub.cc ' when a supply voltage V.sub.cc that ramps up from said predetermined lower threshold voltage V.sub.cc .degree. to said predetermined upper threshold voltage V.sub.cc ' is applied to said power on-reset circuit, said power-on reset circuit comprising:a self-biased current generator that generates a current, which is proportional to a temperature at which said power-on reset circuit is operating, when said supply voltage is applied on said self-biased current generator, said self-biased current generator further comprising;a first current generator BJT (Bipolar Junction Transistor) and a second current generator BJT (Bipolar Junction Transistor) being coupled to each other as a current-mirror with an emitter of said second current generator BJT being coupled to ground via a current generator resistor;wherein said first current generator BJT has a first emitter area, and wherein said second current generator BJT has a second emitter area, and wherein A is a size factor of a ratio of said second emitter area to said first emitter area;and wherein said current generated by said self-biased current generator is a current flowing through said second current generator BJT with a current level substantially equal to [k*T*ln(A)]/[q*R.sub.1 ], wherein q is the electronic charge, k is Boltzmann's constant, T is said temperature at which said power-on reset circuit is operating, and R.sub.1 is a resistance value of said current generator resistor;a base-emitter voltage detector further including:a voltage detector BJT (Bipolar Junction Transistor) having a base coupled to a base of said second current generator BJT of said self-biased current generator such that a current flowing though said voltage detector BJT is substantially equal to said current generated by said self-biased current generator;a first voltage detector resistor coupled between a collector of said voltage detector BJT and said supply voltage, wherein said first voltage detector resistor has a resistance value of R.sub.2 ; anda second voltage detector resistor coupled between said collector of said voltage detector BJT and ground, wherein said second voltage detector resistor has a resistance value of R.sub.3 ; anda bipolar complementary metal oxide semiconductor (BiCMOS) inverter including an inverter BJT (Bipolar Junction Transistor) having a base coupled to said collector of said voltage detector BJT, and said inverter BJT having a collector that generates said power-on reset pulse as said supply voltage is turned on, and said inverter BJT having an emitter coupled to said ground;wherein said inverter BJT stays turned off as said power-on reset pulse at said collector of said inverter BJT linearly ramps up from said predetermined lower threshold voltage V.sub.cc .degree. to said predetermined upper threshold voltage V.sub.cc ';and wherein said inverter BJT turns on when said power-on reset pulse reaches said predetermined upper threshold voltage V.sub.cc ' such that said collector of said inverter BJT is coupled to said ground;and wherein said predetermined upper threshold voltage Vcc' is substantially equal to V.sub.BE *[1+R.sub.2 /R.sub.3 ]+[R.sub.2 /R.sub.1 ]*[k*T*ln(A)]*[1/q], wherein V.sub.BE is a base to emitter voltage (V.sub.BE) of said inverter BJT when said inverter BJT is turned on, and wherein R.sub.2 is said resistance value of said first voltage detector resistor, and wherein R.sub.3 is said resistance value of said second voltage detector resistor.