Summing amplifier

Recall the two rules:

1. No Current Flows into the Input Terminals
2. The Differential Input Voltage is Zero i.e. $V_+ = V_- $

A summing amplifer sums several (weighted) voltages:

               
When , and independent

               
When

                

Digital-to-analog converter:

Let,

• $R_F = 1 K \Omega $
• Logic '0' = 0V
• Logic '1' = 5V

So, for input "0000", the output is $V_{out} = 0$ (since all input = 0V)

For "0001", $V_{out} = -(0+0+0+5/8) = -0.625 V$

For "1101", $V_{out} = -(5/1+5/2+0+5/8) = -8.125 V$

For "1111", $V_{out} = -(5/1+5/2+5/4+5/8) = -9.375 V$

Thus, we get proportionate analog voltage at the output.