An Open-Loop Class-D Audio Amplifier with Increased Low-Distortion Output Power … · 2017. 10....

Paper 8-6

An Open-Loop Class-D Audio Amplifier with Increased

Low-Distortion Output Power and PVT-Insensitive EMI ReductionShih-Hsiung Chien1, Li-Te Wu2, Ssu-Ying Chen2,

Ren-Dau Jan2, Min-Yung Shih2, Ching-Tzung Lin2 and Tai-Haur Kuo1

1National Cheng Kung University, Tainan, Taiwan, 2NeoEnergy Microelectronics, Inc., Hsinchu, Taiwan

2 of 32© 2014 IEEE IEEE Custom Integrated Circuits Conference 2014

Outline Background and Motivation

System Overview

Proposed Techniques Adaptive-Coefficient Delta-Sigma Modulator PVT-Insensitive Low-EMI Control Method

Measurement Results

Conclusions


Digital-Input Audio Amplifier Class-AB amplifier with DAC

Class-D amplifier with DAC

Class-D amplifier with digital PWM (DPWM) gen.

Class-ABAmp.

DigitalInput

SpeakerLoadDAC

Class-DAmp.

Low-PassFilter

DigitalInput

SpeakerLoadDAC

DPWM Class-DAmp.

Low-PassFilter

DigitalInput

SpeakerLoad


Class-D Amplifier with DPWM Pros

High efficiency No need of high-resolution DAC

Cons Distortion from class-D amp. Degraded THD+N Need of L-C low-pass filter for EMI suppression

DPWM Class-DAmp.

Low-PassFilter

DigitalInput

SpeakerLoad


Closed-Loop vs. Open-Loop Closed-loop architecture

Open-loop architecture adopted in this work

Lower complexityEasier design porting to advanced processes

Smaller chip area

DSMPCM-to-PWM

Converter (gain=1)

Analog Loop Filter

Interpo-lator

(gain=1)Digital Input

Power Stage

Feedback Path (feedback factor = β )

clock

DPWM

Low-PassFilter

SpeakerLoad

DSMPCM-to-PWM

Converter (gain=1)

Power Stage

Interpo-lator

(gain=1)Digital Input clock

Low-PassFilter

SpeakerLoad

DPWM


THD+N vs. Output Power Distortion and noise sources

Constant noise Power stage distortion Clip distortion

Low-distortion POUT = max. POUT with THD+N<1% Dominated by clip distortion due to DSM instability

THD

+N (%

)

Output Power, POUT (W)

1%

Low-Distortion POUT


DSM Instability in Open-Loop When DSM input is large DSM’s quantizer overload clipping at DSMOUT clip distortion at amp. output decreased low-distortion output power

Clipping Error

DSMPCM-to-PWM

Converter (gain 1/k=1)

Power Stage

Interpo-lator

(gain k=1)Digital Input

DSMOUT PWMOUTclock

Power Output

Input mag.(dBFS)

SN

DR

(dB)

0

SNDR @ DSMOUT

SN

DR

(dB)

0Input mag.(dBFS)

SNDR @ PWMOUT

1%

Output power(W)

THD

+N(%

)THD+N vs. output power


DSM Instability in Open-Loop To reduce DSM input: interpolator’s gain To increase gain after DSM: PCM-to-PWM’s gain Clipping at PWMOUT

DSM instability can NOT be prevented by scaling kClipping

Error

DSMPCM-to-PWM

Converter (gain 1/k >1)

Power Stage

Interpo-lator

(gain k<1)Digital Input

DSMOUT PWMOUTclock

Power Output

Input mag.(dBFS)

SN

DR

(dB)

0

SNDR @ DSMOUT

SN

DR

(dB)

0Input mag.(dBFS)

SNDR @ PWMOUT

1%

Output power(W)

THD

+N(%

)THD+N vs. output power


Common-Mode EMI Reduction Conventional BD modulation

Common-Mode Free BD (CMFBD) modulation [1]

[1] P. Siniscalchi and R. Hester, “A 20W/channel class-D amplifier with significantly reduced common-mode radiated emissions,” IEEE ISSCC 2009.

VDD/2VDD

0

VDD

0

VDD

0

VCM

OUTN

OUTP

VDD/2VDD

0

VDD/2VDD

0

VDD/2VCM

OUTN

OUTP


Targets of This Work Increase low-distortion output power for open-loop

class-D amplifiers without increasing supply voltage increasing off-chip components sacrificing THD+N at small output power

Reduce common-mode EMI without using expensive L-C filters PVT-sensitive issue


System Overview Block diagram of this work

Two selectable modes BD-Modulation Mode

Delta-Sigma Modulator

(DSM)

PCM-to-PWM

Converter Power Stage

Interpo-latorDigital

Input

OUTP Low-Pass FilterOUTN

Dual-Mode Output Stage

SEL

Proposed ACDSM

x[n] y[n]

AdaptiveCoefficient

Set[n]

OUTP

OUTN

bead

C

bead

LOUTP

OUTN

L

C

Low-EMI Mode [1]


DSMADSMB

20

0

-40

-80

-20

-60

Gai

n (d

B)

0.1 1 10 100 192Frequency (kHz)

Trade-Off in DSM Design Two DSM Designs

DSMA: high in-band noise suppression DSMB: full-scale stable input range

NTF plot Root-locus plot

-1 -0.5 0 0.5 1Real axis

Imag

inar

y ax

isunit circle

DSMADSMB

1

0.5

-0.5

0

-1


Proposed ACDSM Adaptive-Coefficient Delta-Sigma Modulator (ACDSM)

Small x[n] coef. with high in-band noise suppression Large x[n] coef. with full-scale stable input range

g1[n] · H

Quantizer

g2[n] · H g3[n] · H g4[n] · H g5[n] · H

y[n]

x[n]

a1[n] a2[n] a3[n] a4[n] a5[n]

b1[n]

b2[n]

b3[n]

b4[n]


Direct Coefficient Switching Coefficient is switched between

Small x[n] SetA (high in-band noise suppression) Large x[n] SetB (full-scale stable input range)

large internal transient spike DSM unstable

Delta-Sigma Modulator (DSM)

SetB

y[n]x[n]

SetA

SetA = [g1A,...g5A,a1A,...a5A,b1A,...b4A]SetB = [g1B,...g5B,a1B,...a5B,b1B,...b4B]


ACDSM Algorithm Linear-interpolated coefficient changing operating coefficient set is changed with small SetΔ internal transient spike is reduced

N Sets

Delta-Sigma Modulator (DSM)

SetB

SetΔ

y[n]x[n]

Set1 SetN SetA

SetΔ SetΔ SetΔ

Proposed ACDSM Algorithm


Dynamic Range (DR) Plots The ACDSM simultaneously achieves

a wide stable input range high in-band noise suppression

100

80

60-1 -0.5 0

DSMADSMBACDSM

120

-40 -30 -20 -10 0Input Magnitude (dBFS)

SND

R (d

B)

100

80

60

50


CMFBD Realization Previous low-EMI control method [1]

[1] P. Siniscalchi and R. Hester, “A 20W/channel class-D amplifier with significantly reduced common-mode radiated emissions,” IEEE ISSCC 2009.

turn-on:M2, M3

turn-on:M5, M6

turn-on:M1, M4

S1 S2S0

M1M5 M6

M2

M3

M4

OUTP OUTN

VDD

VG1

VG4

VG5 VG6

Speaker Load


Previous Low-EMI Control (1/3) In state S0

turn-on:M2, M3

turn-on:M5, M6

turn-on:M1, M4

S1 S2S0

VG1,VG4

t

t

t

OUTP

OUTN

S0

M1M5 M6

M2

M3

M4

OUTP OUTN

VDD

VG1

VG4

VG5 VG6

Speaker Load

VG5,VG6


Previous Low-EMI Control (2/3) In transition from S0 into S1

turn-on:M2, M3

turn-on:M5, M6

turn-on:M1, M4

S1 S2S0

t

t

tS0

Speaker Load

M1M5 M6

M2

M3

M4

OUTP OUTN

VDD

VG1

VG4

VG5 VG6VG1,VG4

OUTP

OUTN

VG5,VG6


Previous Low-EMI Control (3/3) In state S1

turn-on:M2, M3

turn-on:M5, M6

turn-on:M1, M4

S1 S2S0

t

t

tS0 S1

Speaker Load

M1M5 M6

M2

M3

M4

OUTP OUTN

VDD

VG1

VG4

VG5 VG6VG1,VG4

OUTP

OUTN

VG5,VG6


PVT Variation Effect (1/2) Significant shoot-through current

t

t

t

Speaker Load

M1M5 M6

M2

M3

M4

OUTP OUTN

VDD

VG1

VG4

VG5 VG6Shoot-through

turn-on:M2, M3

turn-on:M5, M6

turn-on:M1, M4

S1 S2S0

VG1,VG4

OUTP

OUTN

VG5,VG6


PVT Variation Effect (2/2) Additional output voltage transition

t

t

t

Speaker Load

M1M5 M6

M2

M3

M4

OUTP OUTN

VDD

VG1

VG4

VG5 VG6

Additional transition

turn-on:M2, M3

turn-on:M5, M6

turn-on:M1, M4

S1 S2S0

VG1,VG4

OUTP

OUTN

VG5,VG6


CMFBD Realization Proposed low-EMI control method

M1M5 M6

M2

M3

M4

OUTP OUTN

VDD

VG1

VG4

VG5 VG6

Speaker Load

turn-on:M2, M3, M6

turn-on:M6

turn-on:M5, M6

turn-on:M5

turn-on:M1, M4, M5

SC SD SESA SB


Proposed Low-EMI Control (1/4) In state SA

M1M5 M6

M2

M3

M4

OUTP OUTN

VDD

VG1

VG4

VG5 VG6

Speaker Load

turn-on:M2, M3, M6

turn-on:M6

turn-on:M5, M6

turn-on:M5

turn-on:M1, M4, M5

SC SD SESA SB

t

t

tSA

t

VG5

OUTP

OUTN

VG6

VG1,VG4


Proposed Low-EMI Control (2/4) In transition from SA into SB

t

t

tSA

t

M1M5 M6

M2

M3

M4

OUTP OUTN

VDD

VG1

VG4

VG5 VG6

Speaker Load

turn-on:M2, M3, M6

turn-on:M6

turn-on:M5, M6

turn-on:M5

turn-on:M1, M4, M5

SC SD SESA SB

VG5

OUTP

OUTN

VG6

VG1,VG4


Proposed Low-EMI Control (3/4) In state SB

t

t

tSA

t

M1M5 M6

M2

M3

M4

OUTP OUTN

VDD

VG1

VG4

VG5 VG6

Speaker Load

turn-on:M2, M3, M6

turn-on:M6

turn-on:M5, M6

turn-on:M5

turn-on:M1, M4, M5

SC SD SESA SB

SB

VG5

OUTP

OUTN

VG6

VG1,VG4


Proposed Low-EMI Control (4/4) In state SC

t

t

tSA

t

SC

M1M5 M6

M2

M3

M4

OUTP OUTN

VDD

VG1

VG4

VG5 VG6

Speaker Load

turn-on:M2, M3, M6

turn-on:M6

turn-on:M5, M6

turn-on:M5

turn-on:M1, M4, M5

SC SD SESA SB

SB

VG5

OUTP

OUTN

VG6

VG1,VG4


Chip Micrograph

2.45 mm

1.5 mm

DSM

M5,6 of L

CH

M5,6 of R

CH

M1 of LCH

M3 of LCH

M2,4 of LCH

M3 of RCH

M1 of RCH

M2,4 of RCH

Gate D

river

DigitalAudio

Processor

0.2 mm

0.3 mm


THD+N vs. Output Power Measurement condition: 24-VDD, 8-Ω, BD modulation 30-W low-distortion output power 20% increase by ACDSM

0.1 0.5 1 5 10 20 30Output power (W)

1.5

THD

+N (%

)

1

0.5

0.1

0.05

DSMADSMBACDSM

1.51

0.5

0.2

0.120 25 30

increased by 5W


EMI Measurement Conducted EMI

Radiated EMI

0.15 0.5 1 5 10 20 30 Frequency (MHz)

60

40

20

Leve

l (dB

μV/m

)

low-EMI modeBD-modulation mode

Frequency (MHz)

60

20

0.15 0.5 1 5 10 20 30

8 dBμV/m

Leve

l (dB

μV/m

)

30 64 98 132 166 200 360 520 680 840 1000Frequency (MHz)

50

30

10

BD-modulation mode

low-EMI mode

FCC class-B standard24 dBμV/m


Comparison

( ) )2/(PowerOutput Normalized 2

LDD

OUT

RVηP

⋅⋅= (1)

g q y ( )

Chip Area (4) (mm2)

Process

3.74 (stereo)0.18μm

BCDMOS

23.9 (5.1-ch)0.35μm

HVCMOS

0.76 (stereo)65nm

CMOS

Supply Voltage VDD (V)Nominal Load RL (Ω)Peak Efficiency η (%)

Output Power POUT (W)@ 1%THD+N

Normalized Output Power (1)

@ 1%THD+NDSM Max. Stable Input

(dBFS)

EMI Reduction (2) (dBμV/m)

This Work

24890

30

1.03

+0.2

8 (conducted)24 (radiated)

(3)

JSSC 2012 [3]18888

13

0.83

-1.2

-

JSSC 2010 [4]3888

0.4

0.92

-0.7

-


Conclusion A 30-W open-loop class-D amplifier is implemented

for a 24-V supply voltage and 8-Ω load

The ACDSM simultaneously achieves high in-band noise suppression wide stable input range 20% low-distortion POUT increase

The proposed low-EMI control method PVT-insensitive common-mode EMI reduction

Date post:	15-Mar-2021
Category:	Documents
Upload:	others
View:	4 times
Download:	0 times

An Open-Loop Class-D Audio Amplifier with Increased Low-Distortion Output Power … · 2017. 10....

Documents