Bandpass sigma-delta modulator

Abstract

A bandpass sigma-delta modulator using acoustic resonators or micro-mechanical resonators. In order to improve resolution at high frequencies, acoustic resonators or micro-mechanical resonators are utilized in a sigma-delta modulator instead of electronic resonators. The quantized output is fed back using a pair of D/A converters to an input summation device. In fourth order devices, the feed back is to two summation devices in series. Such a sigma-delta modulator is usable in a software defined radio cellular telephone system and in other applications where high-frequency and high-resolution A/D conversion is required.

1. A bandpass sigma-delta modulator comprising:
 a summing device for receiving an input and first and second feedback signals and producing an output;  
 a micro-mechanical resonator receiving the output of said summing circuit as an input and producing an output;  
 a quantizer receiving the output of said micro-mechanical resonator and producing a digital output which is the output of said modulator and;  
 first and second D/A converters receiving said output of said quantizer as an input and producing said first and second feedback signals.  
 
     
     
       2. The bandpass sigma-delta modulator according to  claim 1 , wherein gain stages are provided between said first D/A converter and said summing device, between said second D/A converter and said summing device, and between said micro-mechanical resonator and said quantizer. 
     
     
       3. A bandpass sigma-delta modulator comprising:
 a first summing device receiving an input, a first feedback signal and a second feedback signal and producing an output;  
 a first micro-mechanical resonator receiving said output from said first summing device and producing an output;  
 a second summing device receiving said output from said first micro-mechanical resonator and receiving third and fourth feedback signals and producing an output;  
 a second micro-mechanical resonator receiving said output from said second summing circuit and producing an output;  
 a quantizer receiving said output from said second micro-mechanical resonator and producing an output which is the output of said modulator; and  
 first and second D/A converters, each receiving the output of said quantizer as an input, said first D/A converter producing said first and third feedback signals, and said second D/A converter producing said second and fourth feedback signals.  
 
     
     
       4. The bandpass sigma-delta modulator according to  claim 3 , further comprising gain stages between said first micro-mechanical resonator and said second summing device, between said second micro-mechanical resonator and said quantizer, between said first D/A converter and said first summing device, between said first D/A converter and said second summing device, between said second D/A converter and said first summing device and between said second D/A converter and said second summing device. 
     
     
       5. A bandpass sigma- delta modulator, comprising:      a summing device configured to receive an input signal, and produce a first output signal;        a micro - mechanical resonator coupled to the summing device and configured to provide a second output signal based, at least in part, on the first output signal;        a quantizer coupled to the micro - mechanical resonator and configured to provide a digital output signal based, at least in part, on the second output signal; and        first and second D/A converters coupled to the quantizer and configured to produce the first and second feedback signals based, at least in part, on the digital output, wherein the first and second feedback signals affect a gain applied to the input signal.     
     
     
       6. The bandpass sigma- delta modulator of    claim 5   , further comprising one or more gain stages coupled to the first and second D/A converters and configured to apply the gain to the input signal based, at least in part, on the first and second feedback signals.   
     
     
       7. The bandpass sigma- delta modulator of    claim 5   , further comprising:      a first gain stage coupled between the summing device and the first D/A converter;        a second gain stage coupled between the summing device and the second D/A converter; and        a third gain stage coupled between the micro - mechanical resonator and the quantizer.     
     
     
       8. A method, comprising:
   combining an input signal with a first analog feedback signal and a second analog feedback signal to apply a gain to the input signal and to provide a first output signal;        receiving a second output signal from a micro - mechanical resonator, wherein the second output signal is generated based, at least in part, on the first output signal;        quantizing the second output signal to provide a digital output signal based, at least in part, on the second output signal; and        generating the first analog feedback signal and the second analog feedback signal based, at least in part, on the digital output signal.     
     
     
       9. The method of  claim 8 , further comprising employing one or more gain stages to apply the gain to the input signal based, at least in part, on the first analog feedback signal and the second analog feedback signal. 
     
     
       10. A cellular telephone, comprising:
   a software - defined radio configured to receive a digital signal; and        a bandpass sigma - delta modulator including:      a summing device configured to receive an input signal and produce a first output signal;        a micro - mechanical resonator coupled to the summing device and configured to provide a second output signal based, at least in part, on the first output signal;        a quantizer coupled to the micro - mechanical resonator and configured to provide the digital signal based, at least in part, on the second output signal; and        first and second D/A converters coupled to the quantizer and configured to produce first and second feedback signals based, at least in part, on the digital signal, wherein the first and second feedback signals affect a gain applied to the input signal.       
     
     
       11. The cellular telephone of  claim 10 , wherein the bandpass sigma- delta modulator further comprises one or more gain stages coupled to the first and second D/A converters and configured to apply the gain to the input signal based, at least in part, on the first and second feedback signals.   
     
     
       12. The cellular telephone of  claim 10 , wherein the bandpass sigma- delta modulator further comprises:      a first gain stage coupled between the summing device and the first D/A converter;        a second gain stage coupled between the summing device and the second D/A converter; and        a third gain stage coupled between the micro - mechanical resonator and the quantizer.