Www.zetex.com Sub Woofer amplifier solutions An introduction.

www.zetex.com

Sub Woofer amplifier solutions

An introduction

www.zetex.comConfidential

Objectives

Focussed market Quality solution for quality prospects Specific application: Subwoofers

Added value for customers Flexible reference designs Ease of design

Maintain value Competitive BOM cost


Zetex audio product strengths

Audio quality Value what it sounds like Value specifications

Power & efficiency in a small space ‘Mid up’ power (50W to 500W) Smaller amplifiers & speakers Smaller PSUs Less heat

Ease of implementation Integrated features Good support Reference designs


Zetex audio market focus

End product focus AVR (multi-channel) Stereo Subwoofer High end home theatre Powered speakers Distributed audio Pro-audio

Non focus markets Very low power: mobile phone, MP3 player Mid power integrated: flat panel TV, theatre in a box, boom box, PC audio


Zetex subwoofer customer profile

End product brand Recognised quality product Sound commercial & technical opportunity Market influencer

OEM/ODM Visible good link to end brand Already building subwoofer Electronic design capability

Fit Audio: value performance Commercial: channel cost, volume match Technical: specifications, reference designs

Support requirements Priority vs. capacity (time & effort) Use of reference designs & demo boards

Key point:

Try to link these

together


Switching amplifier theory

A general recap on Class D Modulate an input signal with a clock to generate a PWM output Amplify the PWM signal with an H bridge and filter to recover the analogue power signal

The advantages are: 90% efficiency (Class AB at 50%) Less heat dissipation Smaller PSU Cost effective solution

Audio

Triangle

PWM Comparator

PWM Output

Audio

Triangle

PWM Comparator

PWM Output

Audio

Comparator O/P (Duty Cycle = 50%)


Triangle

Output

Audio

Triangle

Output

Audio



Triangle

Output

Audio

Triangle

Output

Triangle inputAudio input

PWM output

Triangle inputAudio input

PWM outputBut it still has to sound good: Zetex does!


Switching amplifier theory

Class AB 50% efficiency For 500W out, need 1kW in

Class D 90% efficiency For 500W out, need 550W in

Power supply

Class ABAmplifier

Audio input

500W500W

1000W

Power supply

Class DAmplifier

Audio input

500W50W

550W

Actually in practice PSU can be smaller still. Typical audio content is 1/8 full power (but still must be able to supply short term full power)


Switching amplifier products

All Zetex switching amplifiers are Class D.

Two types:

Analogue input ZXCD Series based Focus on subwoofer applications Can still support mid power full band applications

Digital input DDFATM is the focus (Class Z) Not ready yet for general release


Analogue input products

Part numbers ZXCD1000/1010

Focus on: ZXCD1210 (New for subwoofers)

Reference designs ZXCD50STEVAL: 50W 4Ω stereo ZXCD100MOEVAL: 100W 4Ω mono ZXCDSUBEV series: 150W to 500W 4Ω mono: (New for subwoofers)


Why Class D for subwoofers?

Subs reproduce deep bass in movie soundtracks Sound you can feel (Explosions, rumbles etc)

Requirement for higher power The ear is less sensitive to low frequencies The trend to smaller cabinets and a requirement to reach a high

sound pressure level (SPL) Sealed cabinets offer no resonant assistance at low frequencies Competition with other speakers (fronts, centre and surrounds)

Subwoofer solution A separate channel for low frequencies: Front end EQ A higher power amplifier: Needs class D for efficiency A self contained amplifier & speaker unit: Includes its own PSU


Subwoofer supply

Home theatre in a box DVD receiver and speakers together More likely to be passive subs

Home theatre speaker sets Higher quality systems Powered or passive subs

Subwoofer separates (most likely target) Powered subs Higher quality systems Higher power Custom install


Subwoofer variants

Downward firing drive unit

Front firing drive unit

Sealed or ported

Passive radiator design Second diaphragm on the back face of the sub

Twin drive unit Two drivers, possibly each with its own amp

Twin voice coil unit Single driver, twin coils, twin amps

AMP

AMPAMP

AMP

AMP

AMP

AMP

AMP


What’s in a powered sub?

Amplifier High power & efficiency, cool

running: Class D Good performance: Damping

factor, THD+N, DNR

Power supply Linear vs. switching Regulated vs. unregulated

Front end processing Analogue audio input Volume, phase, LP/HP filter

Peripherals Short, thermal, DC protection

Power supply

Peripherals

AmplifierFront endAudio

input

HP filter (e.g. 10Hz)

LP filter (e.g. 250Hz)

Phase (e.g. 0 to 180)

Mix & volume


Where does the signal come from?

LFE signal Low frequency effects channel Level preset at +10dB

Bass management signal Mix of low frequency

information filtered from other channels

HPF

HPF

HPF

HPF

HPF

LPF+10dBDecoded AV source Bass Management

Left

Right

Centre

Left sur

Right sur

LFE

Frequency

Bass M’gement

LFE

Main channels

Subwoofer bandwidth


Subwoofer design issues

Damping factor Mass of drive unit and coil back EMF makes it difficult to control Low amplifier output impedance helps significantly Closed loop designs reduce output impedance Ratio of load to amplifier output impedance is the damping factor

Power supply With unregulated supplies, amplifier must accommodate off load

voltages and deal with supply dips Means more headroom in the amp (higher power) and closed loop

amp design (PSRR)

Thermal Subwoofer enclosure plus high power amplifier means lots of heat High efficiency Class D is essential


ZXCDSUBEV series (New) ZXCD1210 based (New) Opportunity for Zetex FETs

ZXMN10A09L3 in 150W design (New) Other Zetex FETs in development

Closed loop BTL (B) and SE (S) designs All N channel output Split power supply rail Optional additional circuits

Zetex sub reference designs

Architecture:


New modulator: ZXCD1210

QFN16 4x4

Bottom view

New device specification:

ZXCD1210JB16 (New)

Developed for ZXCDSUBEV series of reference designs

Performance matched for ZXCDSUBEV reference designs

QFN SM package Smaller space (4mm x 4mm) Thermally efficient (thermal pad)


New FETs: ZXMN10A09

New device specification:

ZXMN10A09L3 (New)

Developed for ZXCDSUBEV150S reference design

FETs for the rest of the reference designs under consideration

TO220 package


Solution value

ZXCDSUBEV BOM cost is approximately $20 in volume

This is low compared to many competitive solutions

Must maintain the value in Zetex BOM content

ZXCD1210 $2

ZXMN10A09 $0.25 (ea)

Note: guide prices only. Always refer back to your local Zetex office


AC feedback Reduces THD+N Increases supply rejection

DC servo Ensures no DC offset

Feedback after inductor Increased damping factor for tighter

bass

ZXCDSUBEV Series

Why closed loop:


Power options: ZXCDSUBEV500B: 500W into 4 ZXCDSUBEV250B: 250W into 4 ZXCDSUBEV150S: 150W into 4

THD+N @ 1W to 400W 0.05%, Dynamic range 98dB Noise floor -135dB Damping factor >285 >90% efficiency Frequency response flat 10Hz

to 250Hz (-3dB @ 5kHz)

ZXCDSUBEV Series

Performance:


ZXCDSUBEV Series

Power options:

Output power (W)

Supply voltage

(±V)

75 150 250 500

25

35

40

ZXCDSUBEV150SSingle ended (SE)ZXCD1210ZXMN10A09

ZXCDSUBEV250BBridge tied load (BTL)ZXCD1210

ZXCDSUBEV500BBridge tied load (BTL)ZXCD1210


ZXCDSUBEV Series

Architecture:

PWMoutput

Output bridge Filter

Audio input

Gate driver

+-

DC Servo

AC comp network

Feedback circuits

Bridge supply

Input buffering and bias

Mute

ZXCD1210 modulator

PWMoutput


Audio input

Gate driver

+-

DC Servo

AC comp network

Feedback circuits

Bridge supply


Mute

ZXCD1210 modulator


THD+N <0.05% @ 1W to 400W

ZXCDSUBEV Series

0.02

0.3

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.22

0.24

0.26

0.28

TH

D+N

(%

)

100m 500200m 500m 1 2 5 10 20 50 100 200

Output Power (W)

0.02

0.3

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.22

0.24

0.26

0.28

TH

D+N

(%

)

100m 500200m 500m 1 2 5 10 20 50 100 200

Output Power (W)

Performance:


Frequency response flat 10Hz to 250Hz

ZXCDSUBEV Series

Performance:

10 5k20 50 100 200 500 1k 2k

Frequency (Hz)

-5

+1

-4.5

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

-0

+0.5

dB

10 5k20 50 100 200 500 1k 2k

Frequency (Hz)

-5

+1

-4.5

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

-0

+0.5

dB


ZXCDSUBEV Series

Design flexibility: Supports PSU options

Unregulated linear: simplestto Regulated switcher: most efficient

Single platform One design supports BTL and SE One design supports power options

Other features added easily Front end: Volume, phase, high/low pass filters Protection: Short circuit, thermal, DC


ZXCDSUBEV Series

Design flexibility:

PWMoutput

ZXCD1210 modulator


Audio input

Gate driver

+-

DC Servo

AC comp network

Feedback circuits


Mute

Protection options:Short circuit, thermal, DC

Bridge options:BTL & SE

Front end options: Volume, phase, filtering

PSU options:Regulated, Unregulated, linear, switching

PWMoutput

ZXCD1210 modulator


Audio input

Gate driver

+-

DC Servo

AC comp network

Feedback circuits


Mute

Protection options:Short circuit, thermal, DC

Bridge options:BTL & SE

Front end options: Volume, phase, filtering

PSU options:Regulated, Unregulated, linear, switching


Zetex subwoofer platform advantage

High performance solution Sound quality advantage High efficiency, cool running Small size Cost effective Single adaptable platform Flexible power range System power supply options Easy addition of value added

features

Www.zetex.com Sub Woofer amplifier solutions An introduction.

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