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High Gain Linearity Continuous-time Programmable Gain Method

IP.com Disclosure Number: IPCOM000237896D
Publication Date: 2014-Jul-18
Document File: 3 page(s) / 263K

Publishing Venue

The IP.com Prior Art Database

Abstract

Programmable gain amplifiers (PGA) are popular in most microcontroller applications. The linearity performance of the PGA is important since it is very difficult to calibrate PGAs over the whole operating range and hence would also contribute to signal distortion. In this paper we propose a method to achieve good linearity using resistors in continuous time domain.

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High Gain Linearity Continuous-time Programmable Gain Method

Abstract

Programmable gain amplifiers (PGA) are popular in most microcontroller applications.  The linearity performance of the PGA is important since it is very difficult to calibrate PGAs over the whole operating range and hence would also contribute to signal distortion.  In this paper we propose a method to achieve good linearity using resistors in continuous time domain.

Introduction

Figure 1 shows a conventional continuous programmable gain method.  In this method, due to the Vinn and Vout value variation, Ron1 and Ron2 will also shift a lot due to the operating point.  Hence the gain from Vinn to Vout may not have good linearity. When using this method, we have to let R>>Ron1/2 to guarantee the linearity across the input common voltage.

 
 

Figure 1. Schematic Diagram of high gain linearity of continuous time PGA structure

 
 

Now we analyze how the Ron1/2 affects the gain linearity.

“n” is programmable gain.

The ideal gain linearity should be “1”, so the derivative of gain linearity should be 0.

Suppose the Ron2=K*Ron1

Equation (5) should be 0 and then we get

After analysis we know that to guarantee the good gain linearity the mux resistance should be proportional to the gain.  Our proposed method uses this conclusion to achieve the high gain linearity gain.

Design and Implementation

Figure 2 shows the implementation of our proposed method.

  1. Box01 is a low offset general purpose amplifier.
  2. Box02 shows p...