Current impulse (CI) digital-to-analog converter (DAC)
A current impulse (CI) method is provided for converting digital data signals to analog values. First, digital data bits are converted into current impulses. Then, the current impulses are converted into analog currents representing the digital data bits. More typically, the method accepts a k-bit digital word, and converts the k-bit digital word into (k) corresponding current impulses. In one aspect, the method accepts (n) consecutive k-bit digital words. Then, for each bit position in the k-bit digital word, (n) consecutive bits are sampled using (n) consecutive phases of an n-phase clock, creating (n) interleaved current impulses. The (n) interleaved current impulses are converted into an analog current representing the (n) consecutive k-bit digital words. Alternatively, (n) consecutive bits are sampled using (n) consecutive phases of an n-phase clock for each bit position in the k-bit digital word, creating (n) summed current impulses. A CI digital-to-analog converter is also provided.
1. A current impulse (CI) digital-to-analog converter (DAC), the CI DAC comprising:
a first switched capacitor circuit having inputs to accept a digital data bit, a first reference voltage, a second reference voltage, and a clock signal, an output connected to a signal ground, and a signal output to supply a current impulse in response to the inputs; and,
a first type II current conveyor (CCII−) having an x terminal to accept the current impulse, a y terminal connected to a signal ground, and a z terminal to supply an analog current responsive to the current impulse.
2. The CI DAC of claim 1 wherein the first CCII is a CCII− and comprises:
a field effect transistor (FET) having a gate connected to a bias voltage, a source connected to the signal output of the first switched capacitor circuit, and a drain to supply the analog current; and,
a current source having a first terminal connected to the FET source and a second terminal connected to the signal ground.
3. The CI DAC of claim 1 wherein the first CCII is a CCII− and comprises:
a bipolar junction transistor (BJT) having a base connected to a bias voltage, an emitter connected to the signal output of the first switched capacitor circuit, and a collector to supply the analog current; and,
a current source having a first terminal connected to the BJT emitter and a second terminal connected to the signal ground.
4. The CI DAC of claim 1 wherein the first switched capacitor circuit comprises:
a capacitor having a first terminal, and a second terminal connected to the signal ground;
a first switch having a first input selectively connected to the first reference voltage, a second input selectively connected to the second reference voltage, a control input to accept the digital data bit, and an output connected to the capacitor first terminal to supply a reference voltage selected in response to the digital data bit; and,
a second switch having the clock signal input to accept the clock signal, an input connected to the capacitor first terminal, and the signal output selectively connected to the capacitor first terminal in response to the clock signal, to supply the current impulse.
5. The CI DAC of claim 1 further comprising:
an array (k) of switched capacitor circuits, each switched capacitor circuit accepting a unique digital data bit from a k-bit digital word, and where each switched capacitor circuit has a signal output connected to the x terminal of the CCII.
6. The CI DAC of claim 5 wherein the switched capacitor circuits supply weighted current impulse values responsive to the significance of the digital data bit in the k-bit digital word.
7. The CI DAC of claim 6 wherein the switched capacitor circuits supply weighted current impulse values in response to an element selected from a group consisting of weighted capacitance values, weighted reference voltages, and combinations thereof.
8. The CI DAC of claim 1 further comprising:
an array (k) of switched capacitor circuits, each switched capacitor circuit accepting a unique digital data bit from a k-bit digital word;
a group of (k) type II current conveyors, where the x terminal of each CCII is connected to the signal output of a corresponding switched capacitor circuit, and where z terminals of the CCIIs in the group are summed to a common analog current node.
9. The CI DAC of claim 8 wherein the switched capacitor circuits supply weighted current impulse values responsive to the significance of the digital data bit in the k-bit digital word.
10. The CI DAC of claim 9 wherein the switched capacitor circuits supply weighted current impulse values in response to an element selected from a group consisting of weighted capacitance values, weighted reference voltages, and combinations thereof.
11. The CI DAC of claim 1 further comprising:
a plurality of (k) switched capacitor circuit arrays, where each array comprises (n) switched capacitor circuits, where each array accepts (n) consecutive data bits for a corresponding bit position in (n) consecutive k-bit digital words, where the (n) switched capacitor circuits in each array are sampled with a corresponding clock phase of an n-phase clock, and where every switched capacitor circuit has a signal output connected to the x terminal of the CCII.
12. The CI DAC of claim 11 wherein the (n) phases of the clock are selected from a group consisting of overlapping or non-overlapping clock phases, where an overlapping clock phase has a rising edge that occurs before a falling edge of a preceding clock phase, and a falling edge that occurs after the rising edge of a subsequent clock phase, and where a non-overlapping clock phase has a rising edge that occurs simultaneously with or after a falling edge of a preceding clock phase, and a falling edge that occurs simultaneously with or before the rising edge of a subsequent clock phase.
13. The CI DAC of claim 1 further comprising:
a plurality of (k) switched capacitor circuit arrays, where each array comprises (n) switched capacitor circuits, where each array accepts (n) consecutive data bits for a corresponding bit position in (n) consecutive k-bit words, where the (n) switched capacitor circuits in each array are sampled with a corresponding phase of an n-phase clock, and where the signal outputs of the switched capacitor circuits in each array are summed at a common corresponding signal output node; and,
a group of (k) type II current conveyors, where the x terminal of each CCII is connected to the common signal output node of a corresponding switched capacitor circuit array, and where z terminals of the CCIIs in the group are summed to a common analog current node.
14. The CI DAC of claim 11 wherein the (n) phases of the clock are selected from a group consisting of overlapping or non-overlapping clock phases, where an overlapping clock phase has a rising edge that occurs before a falling edge of a preceding clock phase, and a falling edge that occurs after the rising edge of a subsequent clock phase, and where a non-overlapping clock phase has a rising edge that occurs simultaneously with or after a falling edge of a preceding clock phase, and a falling edge that occurs simultaneously with or before the rising edge of a subsequent clock phase.
15. The CI DAC of claim 1 further comprising:
a plurality of (m) CI DACs, where the z terminal of each CI DAC has a capacitive output impedance, and where the clock signal input of each CI DAC has a capacitive input impedance;
a signal transmission line having a characteristic impedance with a first terminal connected to a real impedance and a second terminal providing an analog output voltage;
a plurality of (n) clock transmission lines, each clock transmission line having a characteristic impedance with a first end accepting a corresponding phase of an n-phase clock and a second end connected to a real impedance;
wherein the (m) CI DACs are connected to the signal transmission line at (m) locations between the first and second terminals, and the capacitive output impedance of the (m) CI DAC z terminals are absorbed into the characteristic impedance of the signal transmission line; and,
wherein the capacitive input impedance of each CI DAC clock signal input is absorbed into the characteristic impedance of the corresponding clock transmission line.
16. The CI DAC of claim 1 wherein the z terminal of the first CCII supplies a positive component of a pseudo-differential analog current;
the CI DAC further comprising:
a second switched capacitor circuit having inputs to accept a complement of the digital data bit, the first reference voltage, the second reference voltage, and the clock signal, an output connected to the signal ground, and a signal output to supply a current impulse in response to the inputs; and,
a second CCII having an x terminal to accept the current impulse from the second switch capacitor circuit, a y terminal connected to the signal ground, and a z terminal to supply a negative component of the pseudo-differential analog current.
17. A current impulse (CI) method for converting digital data signals to analog values, the method comprising:
accepting a digital data bit;
converting the digital data bit into a current impulse; and,
converting the current impulse into an analog current representing the digital data bit.
18. The method of claim 17 wherein accepting the digital data bit includes accepting a k-bit digital word;
wherein converting the digital data bit into the current impulse includes converting the k-bit digital word into (k) corresponding current impulses; and,
wherein converting the current impulse into the analog current includes converting the (k) current impulses into an analog current representing the k-bit digital word.
19. The method of claim 18 wherein accepting the k-bit digital word includes accepting (n) consecutive k-bit digital words;
wherein converting the k-bit digital word into (k) corresponding current impulses includes, for each bit position in the k-bit digital word, sampling (n) consecutive bits using (n) consecutive phases of an n-phase clock, creating (n) interleaved current impulses; and,
wherein converting the current impulse into the analog current representing the k-bit digital word includes converting the (n) interleaved current impulses into an analog current representing the (n) consecutive k-bit digital words.
20. The method of claim 17 wherein accepting the digital data bit includes accepting a k-bit digital word;
wherein converting the digital data bit into the current impulse includes converting the k-bit digital word into a summed current impulse.
21. The method of claim 20 wherein accepting the k-bit digital word includes accepting (n) consecutive k-bit digital words;
wherein converting the k-bit digital word into a summed current impulses includes, for each bit position in the k-bit digital word, sampling (n) consecutive bits using (n) consecutive phases of an n-phase clock, creating (n) summed current impulses; and,
wherein converting the current impulse into the analog current representing the digital data bit includes converting the (n) summed current impulses into an analog current representing the (n) consecutive digital words.
22. A current impulse (CI) digital-to-analog converter (DAC), the CI DAC comprising:
a switched capacitor circuit having inputs to accept a digital data bit, a first reference voltage, a second reference voltage, and a clock signal, an output connected to a signal ground, and a signal output to supply a current impulse in response to the inputs; and,
a first type II current conveyor (CCII−) comprising:
a field effect transistor (FET) having a gate connected to a bias voltage, a source connected to the signal output of the switched capacitor circuit, and a drain to supply the analog current; and,
a current source having a first terminal connected to the FET source and a second terminal connected to the signal ground.