Non-linear signal amplifiers and uses thereof in a mass spectrometer device

Abstract

Signal amplifiers having a non-linear transfer function. A high speed (high bandwidth) circuit with a non-linear transfer function over a limited range of input signal is provided. By appropriate choice of components, the non-linear transfer function can be used to accurately approximate any monotonic function such as a square root transfer function. In another aspect, a piecewise non-linear circuit arrangement using a set of non-linear sub-circuits is provided to accurately generate a desired non-linear transfer function over an extended dynamic range of input signal. In one implementation of such a circuit, each of the sub-circuits approximates the desired non-linear function over a portion of the input range.

1 . A method of amplifying a mass spectra signal in a mass spectrometer, the method comprising: 
 receiving a transient signal from a signal source, the transient signal having an amplitude proportional to a detected particle flux; and    amplifying the transient signal in a non-linear amplifier having a non-linear transfer function that approximates a square root transfer function to produce an amplified signal having a noise component that is substantially independent of the signal amplitude.    
   
   
       2 . The method of  claim 1 , further comprising converting the amplified signal to a digital output signal using a substantially linear analog-to-digital converter (ADC).  
   
   
       3 . The method of  claim 1 , wherein a sampling interval of the ADC is less than 5.0 ns and wherein the operational bandwidth of the non-linear amplifier is greater than about 100 MHz.  
   
   
       4 . The method of  claim 1 , comprising amplifying the signal to decrease the variation in the amplitude of the noise component of the signal as a function of the amplitude of the signal.  
   
   
       5 . The method of  claim 1 , wherein the non-linear transfer function of the non-linear amplifier is generated at least in part by diode in series with an impedance element.  
   
   
       6 . The method of  claim 1 , wherein the non-linear amplifier includes: 
 two or more circuit elements, each circuit element configured to receive at least a portion of the transient signal and to produce a circuit element output, wherein at least one of said circuit elements has a non-linear transfer function; and    a combining circuit that combines the circuit element outputs to generate the amplified signal.