Abstract: Signal processing circuitry for a bar-coded data input terminal having a bar-code reading device, such as light pen, for reading bar-coded identity data, from bar-coded identity labels, attached to items to be identified for instance takes an output signal from the reading device and derives a processed signal in which changes of signal level are cleaner than corresponding level changes in the output signal. The signal processing circuitry employs a high gain operational amplifier to an input of which the output signal is passed through a capacitor. The amplifier has a capacitor and two diodes, with their conduction directions opposite, connected in parallel between the input and the output of the amplifier, from which an amplified signal opposite to the reading device output signal is delivered. A threshold detector receives the amplified signal and provides a processed signal in which signal level changes in dependence upon the amplified signal passing through threshold levels.