Dual mode sigma delta analog to digital converter and circuit using the same
View Patent ↗The present invention provides a dual mode sigma delta analog to digital converter (ADC), which only in one hardware implementation, used for low IF and near zero IF receiver. The dual mode sigma delta ADC comprises a first switched-capacitor integrator; a second switched-capacitor integrator; a quantizer; a feedback circuit and a mode device. By switching the mode device on or off, one could easily change the configuration of the disclosed ADC to decide the receiving signal falling in low-IF or near zero IF.
1. A dual mode sigma-delta analog-to-digital converter (ADC) comprising:
a first switched-capacitor integrator, for integrating a sum of an input signal and a first feedback signal;
a second switched-capacitor integrator, coupled to the first switched-capacitor integrator for integrating a sum of an output of the first switched-capacitor integrator and a second feedback signal;
a quantizer, having an input terminal coupled to the second switched-capacitor integrator, and an output terminal for providing an output signal of the ADC in at least first and second logic states in response to an output of the second switched-capacitor integrator;
a feedback circuit, coupled to the first switched-capacitor integrator and the second switched-capacitor integrator for providing the first feedback signal to the first switched-capacitor integrator and the second feedback signal to the second switched-capacitor integrator; and
a mode device, coupled to an input terminal of the first switched-capacitor integrator and an output terminal of the second switched-capacitor integrator for providing a mode signal to control an operation of the first switched-capacitor integrator and an operation of the second switched-capacitor integrator.
2. The dual mode sigma-delta ADC of claim 1 , wherein the feedback circuit includes
a first digital-to-analog converter (DAC), coupled to the input terminal of the first switched-capacitor integrator for providing the first feedback signal to the first switched-capacitor integrator; and
a second digital-to-analog converter (DAC), coupled to the input terminal of the second switched-capacitor integrator for providing the second feedback signal to the second switched-capacitor integrator.
3. The dual mode sigma-delta ADC of claim 1 , wherein the mode device comprises:
a first switching element having a first terminal coupled to the input terminal of the first switched-capacitor integrator and a second terminal coupled to the input terminal of the first switched-capacitor integrator;
a second switching element having a first terminal coupled to the input terminal of the first switched-capacitor integrator and a second terminal; and
a third switching element having a first terminal coupled to the second terminal of the second switching element of the mode device and a second terminal coupled to the output terminal of the second switched-capacitor integrator;
wherein the mode device controls the first switching element, the second switching element and the third switching element to be on or off state.
4. The dual mode sigma-delta ADC of claim 3 , wherein between the second switching element and the third switching element, the mode device further comprises:
a fourth switching element having a first terminal coupled to the second terminal of the third switching element and a second terminal;
a fifth switching element having a first terminal coupled to the second terminal of the fourth switching element and a second terminal coupled to the ground;
a first capacitor having a first terminal coupled to the first terminal of the fifth switching element and a second terminal;
a sixth switching element having a first terminal coupled to the second terminal of the first capacitor and a second terminal coupled to the ground; and
a seventh switching element having a first terminal coupled to the first terminal of the sixth switching element and a second terminal coupled to the second terminal of the second switching element.
5. The dual mode sigma-delta ADC of claim 1 , wherein the first switched-capacitor integrator comprises:
a fully-differential operational amplifier, having a first input terminal coupled to the first terminal of the second switching element of the mode device, a second input terminal coupled to the ground and an output terminal; and
a first capacitors, having a first terminal coupled to the first input terminal of the fully-differential operational amplifier of the first switched-capacitor integrator, a second terminal coupled to the output terminal of the fully-differential operational amplifier of the first switched-capacitor integrator.
6. The dual mode sigma-delta ADC of claim 5 , wherein the first switched-capacitor integrator further comprises:
a first switching element having a first terminal coupled to the first terminal of the first switching element and a second terminal;
a second switching element having a first terminal coupled to the second terminal of the first switching element and a second terminal coupled to the ground;
a second capacitor having a first terminal coupled to the first terminal of the second switching element and a second terminal;
a third switching element having a first terminal coupled to the second terminal of the second capacitor and a second terminal coupled to the ground;
a fourth switching element having a first terminal coupled to the second terminal of the third switching element and a second terminal coupled to the input terminal of the fully-differential operational amplifier of the first switched-capacitor integrator;
a fifth switching element having a first terminal coupled to the second terminal of the first switching element and a second terminal;
a sixth switching element having a first terminal coupled to the second terminal of the fifth switching element and a second terminal coupled to the ground;
a third capacitor having a first terminal coupled to the second terminal of the sixth switching element and a second terminal;
a seventh switching element having a first terminal coupled to the second terminal of the third capacitor and a second terminal coupled to the ground;
a eighth switching element having a first terminal coupled to the seventh terminal of the seventh switching element and a second terminal coupled to the input terminal of the fully-differential operational amplifier of the first switched-capacitor integrator.
7. The dual mode sigma-delta ADC of claim 1 , wherein the second switched-capacitor integrator comprises:
a fully-differential operational amplifier, having a first input terminal, a second input terminal coupled to the ground and an output terminal coupled to the input terminal of the quantizer; and
a first capacitor, having a first terminal coupled to the first input terminal of the fully-differential operational amplifier of the second switched-capacitor integrator, a second terminal coupled to the output terminal of the fully-differential operational amplifier.
8. The dual mode sigma-delta ADC of claim 7 , wherein the second switched-capacitor integrator further comprises:
a first switching element having a first terminal coupled to the first terminal of the output terminal of the fully-differential operational amplifier and a second terminal;
a second switching element having a first terminal coupled to the second terminal of the first switching element and a second terminal coupled to the ground;
a second capacitor having a first terminal coupled to the first terminal of the second switching element and a second terminal;
a third switching element having a first terminal coupled to the second terminal of the second capacitor and a second terminal coupled to the ground;
a fourth switching element having a first terminal coupled to the second terminal of the third switching element and a second terminal coupled to the input terminal of the fully-differential operational amplifier of the second switched-capacitor integrator.
9. The dual mode sigma-delta ADC of claim 3 , wherein the first switching element of the mode device is turned on, the second switching element and the third switching element of the mode device are turned off for the dual mode sigma-delta ADC operated in a mode of near zero intermediate frequency (NZIF).
10. The dual mode sigma-delta ADC of claim 3 , wherein the first switching element of the mode device is turned off, the second switching element and the third switching element of the mode device are turned on for the dual mode sigma-delta ADC operated in a mode of low intermediate frequency.
11. A receiver circuit comprising:
a low noise amplifier, having an output terminal;
a synthesizer, having a first output terminal for providing a first signal and a second output terminal for providing a second signal;
a first mixer, having a first input terminal coupled to the output terminal of the low noise amplifier, a second input terminal coupled to the first input terminal of the synthesizer, and an output terminal;
a second mixer, having a first input terminal coupled to the output terminal of the low noise amplifier, a second input terminal coupled to the second input terminal of the synthesizer, and an output terminal;
a lowpass filter, having a first input terminal coupled to the output terminal of the first mixer, a second input terminal coupled to the output terminal of the second mixer, a first output terminal coupled to a first dual mode sigma-delta ADC as disclosed in claim 1 , and a second output terminal coupled to a second dual mode sigma-delta ADC as disclosed in claim 1 .