Oscillator, transmission/reception device for a bus system and method for generating a clock frequency using the oscillator

A transmission/reception device for a subscriber station for a bus system, the transmission/reception device being embodied to transmit or receive a message from at least one further subscriber station of the bus system via the bus system, in which bus system exclusive, collision-free access by a subscriber station to a bus of the bus system is ensured at least at times, the transmission/reception device having an oscillator having a first and a second timing element and a logic element, the first and the second timing element being identically constructed and the logic element being connected between the first and the second timing element, wherein each of the first and second timing elements includes:

• a frequency-determining capacitance for determining the frequency of the clock frequency,
• a current source,
• a charging switch disposed between the current source and the frequency-determining capacitance, and
• a comparator;
• wherein the comparator is configured to detect a threshold voltage to which the frequency-determining capacitance is to be charged;
• wherein the frequency-determining capacitance is charged to the threshold voltage when the charging switch is closed;
• and
• wherein the comparator has a switchable capacitance for offset compensation;
• a switch for short-circuiting the drain and gate of a MOS transistor of the comparator, which MOS transistor serves to detect the threshold voltage, the switch being closed in an offset phase and being opened in a charging phase of the frequency-determining capacitance.

A bus system, comprising:

• a bus;
• and
• at least two subscriber stations that are connected to one another via the bus in such a way that they can communicate with one another;
• at least one of the at least two subscriber stations having a transmission/reception device, the transmission/reception device being embodied to transmit or receive a message from at least one further subscriber station of the bus system via the bus system, in which bus system exclusive, collision-free access by a subscriber station to a bus of the bus system is ensured at least at times, the transmission/reception device having an oscillator having a first and a second timing element and a logic element, the first and the second timing element being identically constructed and the logic element being connected between the first and the second timing element, wherein each of the first and second timing elements includes:
• a frequency-determining capacitance for determining the frequency of the clock frequency,
• a current source,
• a charging switch disposed between the current source and the frequency-determining capacitance, and
• a comparator;
• wherein the comparator is configured to detect a threshold voltage to which the frequency-determining capacitance is to be charged;
• wherein the frequency-determining capacitance is charged to the threshold voltage when the charging switch is closed;
• and
• wherein the comparator has a switchable capacitance for offset compensation;
• a switch for short-circuiting the drain and gate of a MOS transistor of the comparator, which MOS transistor serves to detect the threshold voltage, the switch being closed in an offset phase and being opened in a charging phase of the frequency-determining capacitance.

A method for generating a clock frequency with an oscillator, the oscillator including a timing element that has a frequency-determining capacitance and a comparator, the method comprising:

• compensating for an offset with a switchable capacitance of the comparator;
• detecting, with the comparator, a threshold voltage to which the frequency-determining capacitance is to be charged;
• charging the frequency-determining capacitance by closing a charging switch disposed between the frequency-determining capacitance and a current source;
• determining, with the frequency-determining capacitance, the frequency of the clock frequency;
• short-circuiting the drain and gate of a MOS transistor of the comparator, which MOS transistor serves to detect the threshold voltage, the switch being closed in an offset phase and being opened in a charging phase of the frequency-determining capacitance.