Receiver with variable gain control transimpedance amplifier

Abstract

According to one embodiment, a compact low-power receiver comprises first and second analog circuits connected by a digitally controlled interface circuit. The first analog circuit has a first direct-current (DC) offset and a first common mode voltage at an output, and the second analog circuit has a second DC offset and a second common mode voltage at an input. The digitally controlled interface circuit connects the output to the input, and is configured to match the first and second DC offsets and to match the first and second common mode voltages. In one embodiment, the first analog circuit is a variable gain control transimpedance amplifier (TIA) implemented using a current mode buffer, the second analog circuit is a second-order adjustable low-pass filter, whereby a three-pole adjustable low-pass filter in the compact low-power receiver is effectively produced.

What is claimed is: 
     
         1 . An adjustable low-pass filter (LPF) in a compact low-power receiver, the adjustable LPF comprising:
 a resistance input block; and   a plurality of operational amplifiers, wherein
 an input of at least one of the plurality of operational amplifiers is coupled to an output of the at least one of the plurality of operational amplifiers by at least one capacitor; and 
 a number of the plurality of operational amplifiers does not exceed a number of poles characterizing the adjustable LPF. 
   
     
     
         2 . The adjustable LPF of  claim 1 , wherein the resistance input block includes a network of switchable unit resistors situated between an input of the adjustable LPF and the network. 
     
     
         3 . The adjustable LPF of  claim 1 , wherein the at least one capacitor includes a network of switchable unit capacitors. 
     
     
         4 . The adjustable LPF of  claim 1 , wherein:
 the adjustable LPF includes a two-pole adjustable LPF; and   the number of the plurality of operational amplifiers is two.   
     
     
         5 . The adjustable LPF of  claim 1 , wherein the compact low-power receiver utilizes a three-pole low-pass Chebyshev filter. 
     
     
         6 . The adjustable LPF of  claim 1 , wherein the resistance input block includes:
 a network of switchable unit resistors arranged in series and a parallel array of switchable resistors situated between an input of the adjustable LPF and the network.   
     
     
         7 . The adjustable LPF of  claim 6 , wherein the parallel array and the network include native devices for controlling the switchable resistors and the switchable unit resistors. 
     
     
         8 . A system including the adjustable LPF of  claim 1 , a variable gain control transimpedance amplifier (TIA), and a digitally controlled interface circuit connecting an output of the variable gain control TIA to an input of the adjustable LPF. 
     
     
         9 . The system of  claim 8 , wherein the digitally controlled interface circuit is configured to match a first direct-current (DC) offset and first common mode voltage of the output of the variable gain control TIA to a respective second DC offset and second common mode voltage of the input of the adjustable LPF. 
     
     
         10 . An adjustable low-pass filter (LPF) in a compact low-power receiver, the adjustable LPF comprising:
 a plurality of operational amplifiers, wherein
 an input of at least one of the plurality of operational amplifiers is coupled to an output of the at least one of the plurality of operational amplifiers by at least one capacitor; and 
 a number of the plurality of operational amplifiers does not exceed a number of poles characterizing the adjustable LPF. 
   
     
     
         11 . The adjustable LPF of  claim 10 , wherein the at least one capacitor includes a network of switchable unit capacitors. 
     
     
         12 . The adjustable LPF of  claim 10 , wherein the adjustable LPF includes a two-pole adjustable LPF. 
     
     
         13 . The adjustable LPF of  claim 10 , wherein the number of the plurality of operational amplifiers is two. 
     
     
         14 . The adjustable LPF of  claim 12 , wherein the number of the plurality of operational amplifiers is two. 
     
     
         15 . A system including the adjustable LPF of  claim 10 , a variable gain control transimpedance amplifier (TIA), and a digitally controlled interface circuit connecting an output of the variable gain control TIA to an input of the adjustable LPF. 
     
     
         16 . An adjustable low-pass filter (LPF) in a compact low-power receiver, the adjustable LPF comprising:
 a plurality of operational amplifiers, wherein
 a number of the plurality of operational amplifiers is less than or equal to a number of poles characterizing the adjustable LPF. 
   
     
     
         17 . The adjustable LPF of  claim 16 , wherein the number of the plurality of operational amplifiers is two. 
     
     
         18 . The adjustable LPF of  claim 16 , further comprising:
 a resistance input block that includes a network of switchable unit resistors.   
     
     
         19 . The adjustable LPF of  claim 16 , wherein the compact low-power receiver utilizes a three-pole low-pass Chebyshev filter. 
     
     
         20 . The adjustable LPF of  claim 16 , wherein an input of at least one of the plurality of operational amplifiers is coupled to an output of the at least one of the plurality of operational amplifiers by a capacitor.