Integrated Circuits and Systems group, IIT Madras


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courses:ec330_2013:chargepump [2013/01/17 02:47] (current)
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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
 +  * Analyze the circuit in the figure above. Determine the waveforms V<​sub>​A</​sub>​ and V<​sub>​B</​sub>​ in steady state
 +  * 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. ​