A detector signal processing circuit (1a, 1b, 1c) for processing signals from a detector, the detector being used for detecting a fluorescence X-ray energy response in an X-ray analytical instrument and sending a detector response signal (S-10), the instrument is configured to include an operating mode and a calibration mode, the circuit (1a, 1b, 1c) comprises: a pulse generating pulser configured to provide calibration pulses (S-12) with a pulsing amplitude and a pulser frequency, a single common reference voltage element configured to provide a reference voltage signal, a reference analog to digital converter configured to convert calibration pulses (S-12) to a digital reference pulse value (S-16), at least one amplifier configured to amplify an amplifier input, wherein the amplifier input is, sequentially or simultaneously, calibration pulses (S-12) and the detector response signal (S-10) and an amplifier output configured to provide, respectively, an amplified pulse voltage and an amplified response signal voltage, a processing analog to digital converter configured to digitize the amplified pulse voltage and the amplified response signal voltage to produce a digitized pulse voltage value and a digitized response signal voltage value, respectively, wherein the single common reference voltage element is configured to provide the reference voltage signal to the pulser, the reference analog to digital converter and the processing analog to digital converter, a calibration ratio calculator configured to calculate a calibration ratio of the digitized pulse voltage value to the digital reference pulse value, and, an energy scale corrector configured to calculate an operating mode ratio of the digitized response signal voltage value to the calibration ratio and configured to correct the fluorescence X-ray energy response of the detector based on the operating mode ratio. a pulse generating pulser configured to provide calibration pulses (S-12) with a pulsing amplitude and a pulser frequency, a single common reference voltage element configured to provide a reference voltage signal, a reference analog to digital converter configured to convert calibration pulses (S-12) to a digital reference pulse value (S-16), at least one amplifier configured to amplify an amplifier input, wherein the amplifier input is, sequentially or simultaneously, calibration pulses (S-12) and the detector response signal (S-10) and an amplifier output configured to provide, respectively, an amplified pulse voltage and an amplified response signal voltage, a processing analog to digital converter configured to digitize the amplified pulse voltage and the amplified response signal voltage to produce a digitized pulse voltage value and a digitized response signal voltage value, respectively, wherein the single common reference voltage element is configured to provide the reference voltage signal to the pulser, the reference analog to digital converter and the processing analog to digital converter, a calibration ratio calculator configured to calculate a calibration ratio of the digitized pulse voltage value to the digital reference pulse value, and, an energy scale corrector configured to calculate an operating mode ratio of the digitized response signal voltage value to the calibration ratio and configured to correct the fluorescence X-ray energy response of the detector based on the operating mode ratio.