Saturday, June 1, 2013

2 to 4 level converter in 8-QAM

2 to 4 level converter in 8-QAM


i want to make 2 to 4 level converter for 8-QAM modulation, i'm going to use two digital input to get +/- voltage level, i want the output approximately like this,,

when the input 00=-3 V , 01=-5 V , 10=+3 , 11=+5.

i already have one circuit reference, but i'm still confuse, how do i can get a - voltage ?, because the circuit only can make + voltage, take a look this circuit

simulate this circuit – Schematic created using CircuitLab
Any help would be appreciated :)

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