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Switch Fundamentals Slide 7

DC errors associated with a single CMOS switch in the on state are shown in these figures. When the switch is on, DC performance is affected mainly by the switches RON and leakage current (ILKG). Low resistance circuits are more subject to errors due to RON, while high resistance circuits are affected by leakage currents. A resistive attenuator is created by the RG - RON- RLoad combination which produces a gain error. Not only can RON cause gain errors—which can be calibrated using a system gain trim—but its variation with applied signal voltage (RON modulation) can introduce distortion, for which there is no calibration. The ADG14xx family of parts have the industry’s lowest RON at +/-15V supplies with excellent RON flatness which means less distortion and between channel-to-channel matching for RON. The ILKG flows through the equivalent resistance of RLOAD in parallel with the sum of RG and RON. This slide also gives equations that show how these parameters affect DC performance.

PTM Published on: 2009-07-13