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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

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)

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...