Voltage monitoring

A voltage monitoring circuit portion arranged to monitor a negative supply voltage, said voltage monitoring circuit portion comprising:

• a negative voltage generator arranged to generate the negative supply voltage and to output said negative supply voltage at an output terminal of the negative voltage generator;
• a capacitor having a first capacitor plate and a second capacitor plate, said first capacitor plate being connected to the output terminal of the negative voltage generator, said first capacitor plate being further connected to a reference node via a potential divider comprising first and second resistors connected in series, wherein the potential divider is arranged to produce a monitor voltage at a monitor node between said first and second resistors and wherein the reference node is supplied with a positive predetermined reference voltage;
• and
• a comparator arranged to compare the monitor voltage to a threshold voltage and to produce an output signal having a first value when the monitor voltage is below the threshold voltage and having a second value when the monitor voltage is not below the threshold voltage;
• wherein the negative voltage generator is enabled only when the output signal has its second value and is not enabled only when the output signal has its first value;
• and
• wherein the second capacitor plate is connected to a first input of a sense comparator and to a second reference voltage, said sense comparator having a second input connected to a third reference voltage, said sense comparator being arranged to produce a sense signal having a first value when the voltage at its first input is above the third reference voltage and having a second value when the voltage at its first input is not above the third reference voltage.