GM cell based control loops

Abstract

Various circuit techniques employ a transconductance (gm) cell in control loops to implement circuits such as phase locked loops and delay locked loops that are capable of operating at ultra high frequencies with improved precision and noise performance. The gm cell is designed to operate on an analog input signal with a very small swing and more gradual transition edges. These characteristics allow implementation of high frequency circuits and systems including, for example, transceivers for fiber optic channels, disk driver electronics and the like.

What is claimed is:  
     
         1 . A method for generating an output signal locked to an input signal, the method comprising: 
 receiving at a detector the input signal and a reference signal;    generating a detector output signal indicative of a difference between the input signal and the reference signal;    receiving the detector output signal at a first filter coupled to the detector and providing a filtered detector output signal;    receiving the filtered detector output signal at a transconductance (gm) amplifier coupled to the first filter and providing a current output signal;    receiving the current output signal at a second filter coupled to the gm amplifier and providing a control signal; and    receiving at an oscillator coupled to the second filter the control signal and providing an oscillator signal having a property that is adjusted by the control signal.    
     
     
         2 . The method of. claim 1 , wherein the first filter is a single-pole RC filter.  
     
     
         3 . The method of  claim 1  further comprising: 
 receiving at a divider coupled to the oscillator the oscillator signal and dividing the oscillator signal for generating the reference signal.  
 
     
     
         4 . The method of  claim 1 , wherein the input signal is a serial data stream.  
     
     
         5 . The method of  claim 4 , wherein the serial data stream has a data rate of at least 2.488 GHz.  
     
     
         6 . The method of  claim 1 , wherein the gm amplifier includes a differential amplifier receiving the filtered signal and a current load circuit coupled to the differential amplifier providing the current output signal.  
     
     
         7 . The method of  claim 1 , wherein the detector output signal has a peak-to-peak signal swing of less than one volt.  
     
     
         8 . The method of  claim 1 , wherein the reference signal is a reference clock signal.