Delta-sigma A/D converter
An object of the present invention is to provide a highly accurate delta sigma A/D converter. Disclosed is a delta sigma A/D converter including: a first integration circuit to generate a first signal on the basis of an input signal and a first feedback signal from an output side; a first signal conversion circuit to convert the first signal into a first converted signal; a loop delay compensation circuit to generate a compensation signal and then to output the compensation signal in response to a second feedback signal fed back from the output side at a timing earlier than that of the first feedback signal; an adder circuit to add the first converted signal and the compensation signal; and a comparator to generate a digital signal on the basis of an output signal from the adder circuit. The loop delay compensation circuit includes a compensation signal conversion circuit to generate the compensation signal. The compensation signal conversion circuit and the first signal conversion circuit have the approximately same rate of change in conversion coefficient depending on a temperature.
1. A delta sigma A/D converter comprising:
a first integration circuit to generate a first signal on the basis of an input signal and a first feedback signal from an output side;
a first signal conversion circuit to convert the first signal into a first converted signal;
a loop delay compensation circuit to generate a compensation signal and to output the compensation signal in response to a second feedback signal fed back from the output side at a timing earlier than that of the first feedback signal;
an adder circuit to add the first converted signal and the compensation signal; and
a comparator to generate a digital signal on the basis of an output signal from the adder circuit, wherein
the loop delay compensation circuit includes a compensation signal conversion circuit that generates the compensation signal, and
the compensation signal conversion circuit and the first signal conversion circuit have an approximately same rate of change in conversion coefficient depending on a temperature.
2. The delta sigma A/D converter according to claim 1 , wherein
the compensation signal conversion circuit includes a first MOS transistor that receives a reference signal through a gate terminal thereof and generates the compensation signal,
the first signal conversion circuit includes a second MOS transistor that receives the first signal through a gate terminal thereof, and
a ratio between the conversion coefficients of the compensation signal conversion circuit and the first signal conversion circuit is determined on the basis of a ratio between gate widths of the first MOS transistor and the second MOS transistor.
3. The delta sigma A/D converter according to claim 2 , wherein a circuit configuration of the compensation signal conversion circuit and a circuit configuration of the first signal conversion circuit are identical.
4. The delta sigma A/D converter according to claim 1 , further comprising:
a second integration circuit to generate a second signal on the basis of the first signal; and
a second signal conversion circuit to convert the second signal into a second converted signal, wherein
the second signal is also added in the adder circuit, and
the compensation signal conversion circuit and the second signal conversion circuit have an approximately same rate of change in conversion coefficient depending on a temperature.
5. The delta sigma A/D converter according to claim 2 , wherein the compensation signal conversion circuit is a current-voltage conversion circuit of a differential type including a pair of the first MOS transistors.
6. The delta sigma A/D converter according to claim 5 , wherein the compensation signal conversion circuit further includes a first current mirror to output a difference between currents generated by the pair of the first MOS transistors, respectively.
7. The delta sigma A/D converter according to claim 6 , wherein the compensation signal conversion circuit further includes a second current mirror to generate a first mirror current on the basis of the current outputted from the first current mirror.
8. The delta sigma A/D converter according to claim 7 , wherein the compensation signal conversion circuit further includes a third current mirror to generate a second mirror current on the basis of the first mirror current.
9. The delta sigma A/D converter according to claim 1 , further comprising:
a first latch circuit to output the second feedback signal; and
a second latch circuit to output the first feedback signal.
10. The delta sigma A/D converter according to claim 1 , wherein the delta sigma A/D converter is a continuous-time type.