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 — courses:el3203_2014:chargepump [2014/02/06 03:41] (current) Line 1: Line 1: + ====== Charge pump -ve voltage generator ====== + ===== Goals ===== + * Design a negative voltage generator from a positive supply. ​ + * Design a circuit to get a higher voltage than the available supply + + + ===== Preliminaries ===== + {{vnegchargepump.png?​200}} + + * Analyze the circuit in the figure above. Determine the waveforms V<​sub>​A​ and V<​sub>​B​ in steady state. This requires a careful evaluation of the region of operation of the MOS transistors. ​ + + ===== Experiment ===== + + {{vnegchargepump1.png?​300}} + + * Transistors Mn1 and Mn2 are added to multiplex V<​sub>​A​ and V<​sub>​B​ and result in V<​sub>​out​. Implement this circuit using CD4069 inverters. __Think carefully about which terminal goes where!__ You'll need to use separate ICs for the inverter and the rest of the circuitry because, on a chip, the supply and ground pins are all shorted together. You can use clock frequencies in the tens of kHz range, capacitors in the 10nF range, and a supply of 5V. + + * What is the output voltage V<​sub>​out​ with no load(C<​sub>​L​)?​ and with a constant current load I<​sub>​L? ​ + + * Build and demonstrate a circuit that gives a positive output of approximately twice the power supply wrt ground. + + ===== Applications ===== + + * This is useful when a dual supply is required to be generated from a single supply, such as a battery. Such circuits are used in audio amplifiers which, when operated from a dual supply, have a quiescent output of 0V and hence don't need a bulky ac coupling capacitor. These circuits are also used when a small portion of the IC needs a higher supply voltage, but multiple power supplies can't be used. Examples are flash memories(USB sticks) and EEPROMS which operate from a low voltage supply(3V-5V in a mobile phone/MP3 player) but need a high voltage(~ 15V) for write/​erase. ​