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Digital to Analog Converter By Rushabh Mehta Manthan Sheth

12 Progress Current to Voltage converter V out

1. I-V conversion Using a current mirror and load as ground connected PMOS. Possibly the best way to get linear I-V conversion. We evaluated the use of NMOS/PMOS in diode configuration in all possible ways (Doesn’t work) – Always, non-linearity comes when transistor goes from cut-off to saturation. – So, we need to give a constant fixed biasing.

Simulation Result When all 12 bits are ON => Output voltage = 0.75V When all 12 bits are OFF => Output voltage= 2.5V Total Swing = 2.5V to 0.75V

Binary weighted section design Need unit current sources. From our calculation, we need a maximum total current of 3.84uA from binary weighted 4 LSB bits => unit current source = 256nA.

Binary weighted section design 4 bit LSB binary encoder

Binary encoder simulation result Matches perfectly with what was desired. Swing = 2.5V- 0.75V = 1.75V Voltage change when all 4 bits ON = Output voltage = 2.5V – 6.835mV = 2.4931V

Thermometer encoder design Dummy section 4 Bits 2 Bits LSB MSB Y3 Y2 Y1 Y0 A1A0Y0Y1Y2Y3 001000 011100 101110 111111 Y0 = VDD Y1= A1+A0 Y2= A1 Y3= A1.A0

Thermometer encoder design A0A1 Y1 Y2 Y3

Thermometer encoder simulation result A1 A0 Y1 Y2 Y3

Next Designing unit current sources for the thermometer coded section. Level inverter and shifter after I-V conversion. Designing delay block at the input of binary encoder.

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