A signal generator configured to apply a PWM-modulated voltage signal (Vpwm) to an electrical load (LED1,..., LEDn; 12), the PWM-modulated signal (Vpwm) swinging between a high value (Von) and a low value (Voff), wherein both said high value (Von) and said low value (Voff) are non-zero values having a same sign, the signal generator comprising: a first node and a second node configured to have said electrical load coupled therebetween, a first dc voltage generator arranged intermediate said first node and a ground, a second dc voltage generator arranged intermediate said second node and ground or intermediate said second node and said first node, and a PWM modulator switch, characterised in that the PWM modulator switch is arranged intermediate said second node and ground, the PWM modulator switch configured to alternately: couple the second node to ground, wherein a high value (Von) of the PWM-modulated signal (Vpwm) is applied between the first node and the second node from the first dc voltage generator, decouple the second node from ground, wherein a low value (Voff) of the PWM-modulated signal (Vpwm) is applied between the first node and the second node, wherein the low value (Voff) of the PWM-modulated signal (Vpwm) is a function of: the difference of the voltage from the first voltage generator and the voltage from the second voltage generator with said second voltage generator arranged intermediate said second node and ground, or the voltage from the second voltage generator with said second voltage generator arranged intermediate said second node and said first node. a first node and a second node configured to have said electrical load coupled therebetween, a first dc voltage generator arranged intermediate said first node and a ground, a second dc voltage generator arranged intermediate said second node and ground or intermediate said second node and said first node, and a PWM modulator switch, characterised in that the PWM modulator switch is arranged intermediate said second node and ground, the PWM modulator switch configured to alternately: couple the second node to ground, wherein a high value (Von) of the PWM-modulated signal (Vpwm) is applied between the first node and the second node from the first dc voltage generator, decouple the second node from ground, wherein a low value (Voff) of the PWM-modulated signal (Vpwm) is applied between the first node and the second node, wherein the low value (Voff) of the PWM-modulated signal (Vpwm) is a function of: the difference of the voltage from the first voltage generator and the voltage from the second voltage generator with said second voltage generator arranged intermediate said second node and ground, or the voltage from the second voltage generator with said second voltage generator arranged intermediate said second node and said first node. couple the second node to ground, wherein a high value (Von) of the PWM-modulated signal (Vpwm) is applied between the first node and the second node from the first dc voltage generator, decouple the second node from ground, wherein a low value (Voff) of the PWM-modulated signal (Vpwm) is applied between the first node and the second node, wherein the low value (Voff) of the PWM-modulated signal (Vpwm) is a function of: the difference of the voltage from the first voltage generator and the voltage from the second voltage generator with said second voltage generator arranged intermediate said second node and ground, or the voltage from the second voltage generator with said second voltage generator arranged intermediate said second node and said first node. the difference of the voltage from the first voltage generator and the voltage from the second voltage generator with said second voltage generator arranged intermediate said second node and ground, or the voltage from the second voltage generator with said second voltage generator arranged intermediate said second node and said first node.