Integrated Circuits and Systems group, IIT Madras

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courses:ee3703_2017:chargepump [2017/01/10 09:36]
courses:ee3703_2017:chargepump [2017/01/10 09:36] (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
  
 +
 +
 +===== Preliminaries =====
 +{{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. 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</​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. ​