Passive switched-capacitor filters conforming to power constraint

Abstract

Passive switched-capacitor (PSC) filters are described herein. In one design, a PSC filter implements a second-order infinite impulse response (IIR) filter with two complex first-order IIR sections. Each complex first-order IIR section includes three sets of capacitors. A first set of capacitors receives a real input signal and an imaginary delayed signal, stores and shares electrical charges, and provides a real filtered signal. A second set of capacitors receives an imaginary input signal and a real delayed signal, stores and shares electrical charges, and provides an imaginary filtered signal. A third set of capacitors receives the real and imaginary filtered signals, stores and shares electrical charges, and provides the real and imaginary delayed signals. In another design, a PSC filter implements a finite impulse response (FIR) section and an IIR section for a complex first-order IIR section. The IIR section includes multiple complex filter sections operating in an interleaved manner.

What is claimed is: 
     
         1 . A method comprising:
 obtaining multiple coefficients for a filter transfer function;   scaling at least one of the multiple coefficients based on a power constraint for a passive switched-capacitor (PSC) filter; and   implementing the PSC filter based on the at least one scaled coefficient to obtain the filter transfer function.   
     
     
         2 . The method of  claim 1 , wherein the filter transfer function is for a finite impulse response (FIR) filter, and wherein the scaling at least one of the multiple coefficients comprises
 determining a scaling factor based on magnitude of each of the multiple coefficients, and   scaling each of the multiple coefficients based on the scaling factor to obtain a corresponding scaled coefficient.   
     
     
         3 . The method of  claim 2 , wherein the filter transfer function is for a second-order FIR filter, and wherein the power constraint comprises
   | b   0   ′|+|b   1   ′|+|b   2 ′|=1,
   
       where b 0 ″, b 1 ′ and b 2 ′ are three scaled coefficients for the second-order FIR filter. 
     
     
         4 . The method of  claim 1 , wherein the filter transfer function is for an infinite impulse response (IIR) filter, and wherein the scaling at least one of the multiple coefficients comprises
 replacing one of the multiple coefficients with a new coefficient determined based on magnitude of each remaining coefficient.   
     
     
         5 . The method of  claim 4 , wherein the filter transfer function is for a second-order IIR filter, and wherein the power constraint comprises
   | c   0   ′|+|c   1   |+|c   2 |=1,   
       where c 0 ′ is the new coefficient and c 1  and c 2  are two coefficients for the second-order IIR filter. 
     
     
         6 . An apparatus comprising:
 means for obtaining multiple coefficients for a filter transfer function;   means for scaling at least one of the multiple coefficients based on a power constraint for a passive switched-capacitor (PSC) filter; and   means for implementing the PSC filter based on the at least one scaled coefficient to obtain the filter transfer function.   
     
     
         7 . The apparatus of  claim 6 , wherein the filter transfer function is for a finite impulse response (FIR) filter, and wherein the means for scaling at least one of the multiple coefficients comprises
 means for determining a scaling factor based on magnitude of each of the multiple coefficients, and   means for scaling each of the multiple coefficients based on the scaling factor to obtain a corresponding scaled coefficient.   
     
     
         8 . The apparatus of  claim 6 , wherein the filter transfer function is for an infinite impulse response (IIR) filter, and wherein the means for scaling at least one of the multiple coefficients comprises
 means for replacing one of the multiple coefficients with a new coefficient determined based on magnitude of each remaining coefficient.   
     
     
         9 . A computer program product, comprising:
 a computer-readable medium comprising:
 code for causing at least one computer to obtain multiple coefficients for a filter transfer function; 
 code for causing the at least one computer to scale at least one of the multiple coefficients based on a power constraint for a passive switched-capacitor (PSC) filter; and 
 code for causing the at least one computer to implement the PSC filter based on the at least one scaled coefficient to obtain the filter transfer function. 
   
     
     
         10 . A method comprising:
 decomposing a filter transfer function into multiple complex first-order filter sections; and   implementing the multiple complex first-order filter sections with multiple passive switched-capacitor (PSC) filter sections to obtain the filter transfer function.   
     
     
         11 . The method of  claim 10 , wherein the decomposing the filter transfer function comprises
 decomposing the filter transfer function for a second-order infinite impulse response (IIR) filter into two complex first-order IIR sections.   
     
     
         12 . The method of  claim 11 , wherein the decomposing the filter transfer function further comprises
 determining complex coefficients for the two complex first-order IIR sections based on coefficients for the filter transfer function.   
     
     
         13 . The method of  claim 12 , wherein the decomposing the filter transfer function further comprises
 determining an input coefficient for the two complex first-order IIR sections based on magnitude of real and imaginary parts of the complex coefficients.   
     
     
         14 . A method comprising:
 decomposing a filter transfer function into a finite impulse response (FIR) part and an infinite impulse response (IIR) part; and   implementing the FIR part and the IIR part with passive switched-capacitor (PSC) filter sections to obtain the filter transfer function.   
     
     
         15 . The method of  claim 14 , wherein the decomposing the filter transfer function comprises
 decomposing the filter transfer function for a complex first-order IIR filter into the FIR part and the IIR part, and   determining a complex coefficient for the IIR part based on a complex coefficient for the complex first-order IIR filter.   
     
     
         16 . The method of  claim 15 , wherein the complex coefficient for the IIR part is p M , where p is the complex coefficient for the complex first-order IIR filter and M is an integer greater than one. 
     
     
         17 . The method of  claim 14 , wherein the decomposing the filter transfer function comprises
 partitioning the IIR part into multiple (M) IIR sections, each IIR section operating at 1/M clock rate, the M IIR sections being sequentially enabled in M clock cycles.   
     
     
         18 . The method of  claim 14 , wherein the decomposing the filter transfer function comprises
 partitioning the IIR part into first and second IIR sections, the first IIR section being enabled in even-numbered clock cycles, and the second IIR section being enabled in odd-numbered clock cycles.