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| + | ====== 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 | ||
| + | {{vnegchargepump.png?200}} | ||
| + | |||
| + | * Analyze the circuit in the figure above. Determine the waveforms V<sub>A</sub> and V<sub>B</sub> in steady state | ||
| + | |||
| + | {{vnegchargepump1.png?300}} | ||
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| + | * Transistors Mn1 and Mn2 are added to multiplex V<sub>A</sub> and V<sub>B</sub> and result in V<sub>out</sub>. 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</sub> with no load(C<sub>L</sub>)? and with a constant current load I<sub>L</sub>? | ||
| + | |||
| + | * 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. | ||