Semiconductor device
A semiconductor device according to an aspect of the invention relates to an AD converter that converts a signal level of an analog signal into a digital value by using a comparator, and determines an amount of adjustment of an offset voltage of the comparator based on an offset determination result of the comparator obtained immediately after a least significant bit (LSB) of a digital value output as a conversion result is converted.
1. A semiconductor device comprising:
a sample-and-hold circuit that samples an input signal, outputs differential voltages to a first comparison line and to a second comparison line;
a comparator that outputs an output value according to a voltage difference between the first comparison line and the second comparison line;
a digital-to-analog conversion circuit that changes the differential voltages of the first comparison line and the second comparison line according to the output value;
a successive approximation control circuit that controls the sample-and-hold circuit, the comparator, and the digital-to-analog conversion circuit according to a preset successive approximation sequence, and outputs a plurality of output bits as a conversion result of the input voltage; and
a switch circuit that is provided between the first comparison line and the second comparison line, and that is switched by the successive approximation control circuit,
wherein, when the conversion result is acquired, the successive approximation control circuit switches the switch circuit into a conductive state, and outputs control signal to adjust an input offset voltage of the comparator according to the output bits while the switch circuit is in the conductive state, and
wherein the comparator changes the input offset voltage according to the control signal.
2. The semiconductor device according to claim 1 , further comprising:
an offset control circuit that receives the control signal from the successive approximation control circuit and outputs an offset control value to the comparator to change the input offset voltage,
wherein the comparator includes:
a pre-amplifier that amplifies the voltage difference between the first comparison line and the second comparison line, and outputs a first intermediate output voltage and a second intermediate output voltage,
a latch circuit that determines a logic level of the output value according to the first intermediate output voltage and the second intermediate output voltage,
a first offset adjustment capacitor connected to a first intermediate voltage line through which the first intermediate output voltage is transmitted from the pre-amplifier to the latch circuit, and
a second offset adjustment capacitor connected to a second intermediate voltage line through which the second intermediate output voltage is transmitted from the pre-amplifier to the latch circuit,
wherein a capacitance ratio between the first offset adjustment capacitor and the second offset adjustment capacitor changes according to the offset control value.
3. The semiconductor device according to claim 2 , wherein the control signal controls the input offset voltage of the comparator to increase or decrease.
4. The semiconductor device according to claim 2 , wherein the offset control circuit updates the offset control value after the output bits are generated.
5. The semiconductor device according to claim 2 , wherein the offset control circuit updates the offset control value after a preset number of cycles of generating the output bits.
6. The semiconductor device according to claim 5 , wherein the offset control circuit changes the number of cycles after the offset control value is updated.
7. The semiconductor device according to claim 5 , wherein the offset control circuit determines the control value according to a ratio between a number of positive determinations and a number of negative determinations of the preset number of cycles.