Differential amplifier with any number of inputs

Wherever voltage signals are to be amplified, operational amplifiers (op-amp) are used. An op-amp is used to compare, convert and amplify signals. They are therefore among the most important components in analog circuit and measurement technology.

State of the art

Common op-amps have three stages and are equipped with two signal inputs and one output. In the input stage, the differential voltage between the inputs is formed by a differential amplifier (diff-amp), amplified in the voltage amplifier stage and buffered in the output stage to provide a low-impedance output signal. Circuits with more than two independent inputs have so far only been realized by interconnecting several op-amps, resulting in deterioration of characteristic values and increased component costs.

Technology

Scientists from the Electrotechnical Institute (ETI) replaced the classic diff-amp with a diff-amp with any number of even-numbered inputs. In this case, one inverting and one non-inverting input is always added in pairs, without the runtime of the signals being influenced by the amplifier. When amplifying, any inverting input is used to set the amplification and the other inputs are assigned with the input signals. The signal inputs are decoupled from each other by their high input impedance. Thus, a single amplifier circuit can simultaneously sample, sum or subtract a large number of analog signals with high impedance and amplify them by a predetermined factor without affecting the characteristics of the circuit. The new circuit thus ensures high input impedances, high bandwidth, high slew rate and short dead times.

Advantages

The concept allows several conventional interconnected op-amps to be replaced by a single amplifier circuit. This allows common circuits such as instrumentation amplifiers, bridge circuits, measuring amplifiers, filters, etc. to be simplified and/or improved. Due to the optional number of inputs, new application possibilities arise which could not be realized with previous circuits or only with greater component expenditure.

Options for companies

In addition to amplifiers for signal processing, highly dynamic power amplifiers can also be built using an H-bridge circuit. KIT is looking for partners for further development or licensing.