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Open Loop Voltage Gain Linearization of a Single Ended Primary Inductance Converter (SEPIC)

IP.com Disclosure Number: IPCOM000013173D
Original Publication Date: 2003-Jun-17
Included in the Prior Art Database: 2003-Jun-17
Document File: 2 page(s) / 39K

Publishing Venue

Motorola

Related People

D.R. Anderson: AUTHOR

Abstract

Application of Buck PWM converters for Class-S amplifiers is well known. For high frequency Class-S applications above 1 Mhz, application of the SEPIC instead of the Buck converter can result in enhanced amplifier stability and lower cost. To realize these advantages, a ramp function is presented which improves the linearity of the SEPIC’s open loop voltage gain transfer function.

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Open Loop Voltage Gain Linearization of a Single Ended Primary Inductance Converter (SEPIC)

By D.R. Anderson

Motorola, Inc.

 

ABSTRACT

Application of Buck PWM converters for Class-S amplifiers is well known. For high frequency Class-S applications above 1 Mhz, application of the SEPIC instead of the Buck converter can result in enhanced amplifier stability and lower cost. To realize these advantages, a ramp function is presented which improves the linearity of the SEPIC’s open loop voltage gain transfer function.  

PROBLEM

Figure 1 shows a SEPIC Class-S amplifier block diagram and associated linear ramp and PWM waveforms.

Figure 1.

Driven with the linear ramp function Vr(t), the SEPIC Class-S amplifier output voltage is given by equation (1) below:

                (1)

=

Equation (1) clearly shows the non-linear relationship between input voltage signal Vi(t) and output Vo(t).

One potential solution to achieve SEPIC linearization would involve predistortion of the Class-S amplifier input signal Vi(t). A digital predistortion algorithm that linearizes equation (1) could be realized in DSP or implemented in an ASIC. An analog predistorter could also be built; however to be useful with most input modulating signals Vi(t), this circuit would have to perform accurate companding of Vi(t) over a 20dB dynamic range and possess flat frequency response over 5-7 times the bandwidth of Vi(t). In either case, both analog and digital predistortion of Vi(t) will introduce significant processing delay and complexity to the signal path of the Class-S SEPIC amplifier.

Solution

                    Another approach to achieve SEPIC linearization does not require modifications to the signal Vi(t) or the signal path at all.  It is possible to modify the ramp function Vr(t) to accomplish linearization of the SEPIC’s voltage gain.  If the input signal Vi(t) is related to the duty cycle D (d...