A device comprising - at least one photoconductor configured for exhibiting an electrical resistance R photo dependent on an illumination of a light-sensitive region of the photoconductor ; - at least one photoconductor readout circuit , wherein the photoconductor readout circuit is configured for determining the electrical resistance R photo of the photoconductor , wherein the photoconductor readout circuit comprises at least one bias voltage source configured for applying at least one modulated bias voltage to the photoconductor , wherein the bias voltage is a periodical time-dependent bias voltage, wherein the bias voltage is selected such that an integral of charge carriers which flows through the photoconductor over a measurement period is zero, wherein the measurement period is defined by a time between two consecutive transitions of a bias voltage polarization in the same direction, wherein the device comprises at least one first electronic circuit, wherein the first electronic circuit is configured for generating at least one first output signal, wherein a frequency of the first output signal is a mathematical function of said measurement period of the photoconductor , characterized in that the device comprises at least one second photoconductor configured for exhibiting an electrical resistance R photo2 dependent on an illumination of its light-sensitive region, wherein the device comprises at least one second electronic circuit configured for generating a second measurement period, wherein the second electronic circuit is configured for generating at least one second output signal, wherein a frequency of the second output signal is a mathematical function of the measurement periods of the photoconductor and of the second photoconductor , wherein the second electronic circuit is a frequency mixer. - at least one photoconductor configured for exhibiting an electrical resistance R photo dependent on an illumination of a light-sensitive region of the photoconductor ; - at least one photoconductor readout circuit , wherein the photoconductor readout circuit is configured for determining the electrical resistance R photo of the photoconductor , wherein the photoconductor readout circuit comprises at least one bias voltage source configured for applying at least one modulated bias voltage to the photoconductor , wherein the bias voltage is a periodical time-dependent bias voltage, wherein the bias voltage is selected such that an integral of charge carriers which flows through the photoconductor over a measurement period is zero, wherein the measurement period is defined by a time between two consecutive transitions of a bias voltage polarization in the same direction, wherein the device comprises at least one first electronic circuit, wherein the first electronic circuit is configured for generating at least one first output signal, wherein a frequency of the first output signal is a mathematical function of said measurement period of the photoconductor , characterized in that the device comprises at least one second photoconductor configured for exhibiting an electrical resistance R photo2 dependent on an illumination of its light-sensitive region, wherein the device comprises at least one second electronic circuit configured for generating a second measurement period, wherein the second electronic circuit is configured for generating at least one second output signal, wherein a frequency of the second output signal is a mathematical function of the measurement periods of the photoconductor and of the second photoconductor , wherein the second electronic circuit is a frequency mixer. <EOS>