"front":"What is the primary function of a summing amplifier?","back":"To combine multiple input voltages into a single output voltage.","points":1,"mcqOptions":[{"text":"To combine multiple input voltages into a single output voltage.","correct":true,"explanation":"A summing amplifier uses an operational amplifier and several input resistors to produce one output determined by the combined, weighted contributions of the input voltages."},{"text":"To select the largest input voltage as the single output voltage.","correct":false,"explanation":"Selecting whichever input voltage is greatest is the function of a comparator or maximum-selector circuit. A summing amplifier instead combines contributions from all input voltages into one output."},{"text":"To maintain a constant output voltage despite changing input voltages.","correct":false,"explanation":"Holding the output at a fixed level describes voltage regulation rather than summation. A summing amplifier produces an output based on the combined values of multiple input voltages."},{"text":"To subtract one input voltage from another input voltage.","correct":false,"explanation":"A differential amplifier determines the difference between input voltages. A summing amplifier instead combines multiple input voltages, with each input potentially weighted by its resistor value."}]},{"id":"4aa97fee-c86b-47bb-af5d-acdfab792c9c","cardType":"basic","front":"Why is the junction in a summing amplifier referred to as a virtual earth?","back":"

The non-inverting input is grounded ($0 \\text{ V}$)
Infinite open-loop gain forces the inverting input to match this voltage

","points":2,"mcqOptions":[{"text":"

The non-inverting input is grounded ($0 \\text{ V}$)
Infinite open-loop gain forces the inverting input to match this voltage

","correct":true,"explanation":"Negative feedback and the op-amp’s extremely large open-loop gain keep the two input potentials almost equal. Since the non-inverting input is grounded, the inverting junction remains close to $0 \\text{ V}$."},{"text":"

The non-inverting input is connected to the positive supply
Infinite open-loop gain forces the inverting input to match this voltage

","correct":false,"explanation":"Connecting the non-inverting input to the positive supply would establish a virtual reference near that supply voltage, not a virtual earth. For virtual earth, it is grounded and feedback holds the inverting input near $0 \\text{ V}$."},{"text":"

The non-inverting input is grounded ($0 \\text{ V}$)
Infinite open-loop gain forces the inverting input to oppose this voltage

","correct":false,"explanation":"Negative feedback does not make the input voltages equal and opposite; it makes them approximately equal. With the non-inverting input grounded, the inverting junction is consequently held close to $0 \\text{ V}$."},{"text":"

The inverting input is physically grounded ($0 \\text{ V}$)
Infinite input resistance forces every input current to equal zero

","correct":false,"explanation":"The inverting junction is not physically connected to earth, and currents through its input resistors are generally non-zero. It is virtual earth because feedback holds its voltage near that of the grounded non-inverting input."}]}]}],"examCountdown":{"examDate":"2027-05-21","paperLabel":"Paper 1"},"heading":"summing amplifier configuration (A-level only)","title":"summing amplifier configuration (A-level only) Flashcards","topicSidebar":"$L41"}]}],"topicId":"dee8eced-95b7-59b9-8f61-72b04114bdde","walled":"$L42"}],"$L43"]