Integrated rc filter

Abstract

An integrated RC filter includes a first resistor that is coupled to a first capacitor through a first node, a signal input of the integrated RC filter being coupled through one of the first resistor and the first capacitor to the first node. To allow for an increase in the RC timeconstant τ of the RC filter without losing signal transparency, an amplifier is included between the signal input and one of the first resistor and the first capacitor having a gain factor substantially larger than unity, the first node being coupled through an attenuator to a signal output, the attenuator having an attenuation factor substantially corresponding to the amplifier's gain factor.

1 . An integrated RC filter comprising:
 a first capacitor   a first resistor that is coupled to the first capacitor through a first node, a signal input of the integrated RC filter being coupled through one of the first resistor and the first capacitor to the first node,   an amplifier that is coupled between the signal input and the one of the first resistor and the first capacitor, and has a fixed gain factor substantially larger than unity, and   an attenuator that couples the first node to a signal output, and has a fixed attenuation factor to provide the RC filter with a fixed gain between the signal input and the signal output.   
   
   
       2 . The integrated RC filter as claimed in  claim 1 , wherein
 the attenuator includes
 a buffer stage followed by 
 a resistive voltage divider, 
   the buffer stage having an input impedance substantially higher than its output impedance and   the resistive voltage divider having an input impedance substantially equal to the output impedance of the buffer stage.   
   
   
       3 . The integrated RC filter as claimed in  claim 2 , wherein
 the buffer stage comprises one of:
 an emitter follower transistor stage and 
 a source follower transistor stage. 
   
   
   
       4 . The integrated RC filter as claimed in  claim 1 , wherein:
 the signal input is subsequently coupled through the amplifier and the first capacitor to the first node, and   the first node is coupled through the first resistor to a DC reference voltage, and through the attenuator to the signal output.   
   
   
       5 . The integrated RC filter as claimed in  claim 1 , wherein
 the signal input is coupled through the amplifier and the first resistor to the first node, and   the first node is coupled through the first capacitor to a DC reference voltage and through the attenuator to the signal output.   
   
   
       6 . The integrated RC filter of  claim 1 , wherein the fixed gain of the RC filter is substantially unity. 
   
   
       7 . The integrated RC filter of  claim 6 , wherein the fixed gain factor of the amplifier is substantially greater than unity. 
   
   
       8 . The integrated RC filter of  claim 7 , wherein the fixed attenuation factor is substantially greater than unity. 
   
   
       9 . The integrated RC filter of  claim 6 , wherein the fixed attenuation factor is substantially greater than unity. 
   
   
       10 . The integrated RC filter of  claim 6 , wherein the fixed gain factor of the amplifier is substantially equal to a maximum gain factor achievable by the amplifier. 
   
   
       11 . The integrated RC filter of  claim 1 , wherein the fixed gain factor of the amplifier is substantially greater than unity. 
   
   
       12 . The integrated RC filter of  claim 10 , wherein the fixed attenuation factor is substantially greater than unity. 
   
   
       13 . The integrated RC filter of  claim 1 , wherein the fixed attenuation factor is substantially greater than unity. 
   
   
       14 . The integrated RC filter of  claim 1 , wherein the fixed gain factor of the amplifier is substantially equal to a maximum gain factor achievable by the amplifier. 
   
   
       15 . The integrated RC filter of  claim 1 , wherein the resistor value R and capacitor value C are selected to provide an RC time constant using values of R and C that minimize surface area of the integrated RC filter. 
   
   
       16 . The integrated RC filter of  claim 1 , including a DC feedback loop from an output of the attenuator to an input of the amplifier. 
   
   
       17 . The integrated RC filter of  claim 1 , wherein the signal input includes a differential pair, the amplifier includes a differential input and differential output, and the attenuator includes a differential input. 
   
   
       18 . The integrated RC filter of  claim 17 , wherein the differential output of the amplifier is DC balanced. 
   
   
       19 . The integrated RC filter of  claim 18 , including a supply voltage input, wherein the amplifier is DC balanced to a voltage that is substantially half the supply voltage input. 
   
   
       20 . The integrated RC filter of  claim 17 , wherein the amplifier includes a pair of transconductance amplifiers.