The CCA outputs are summed by shorting them directly together. A buffer amplifier stage provides the appropriate output level and impedance. Block diagram of the interpolating scanner. Figure 2 below shows the details of the Scanner Drive circuit. Figure 3 below show the details of the CCAs and buffer amp.
Scanner drive schematic.
The circuit below shows schematics of the CCAs and the buffer amp. Current Controlled Amplifier and Buffer Amp. The issue in extending a diff amp to more than two inputs is to not only gradually turn one transistor off and another on, but also turn that second one off and the next one on in the same manner. Resistors R9 through R14 provide 190mV voltage steps up from the control voltage and resistors R15 through R20 provide 190mV voltages steps up from ground. The diodes select the higher of the two values.