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Sub Woofer amplifier solutions
An introduction
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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
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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
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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
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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
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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%)
Comparator O/P (Duty Cycle = 75%)
Triangle
Output
Audio
Triangle
Output
Audio
Comparator O/P (Duty Cycle = 50%)
Comparator O/P (Duty Cycle = 75%)
Triangle
Output
Audio
Triangle
Output
Triangle inputAudio input
PWM output
Triangle inputAudio input
PWM outputBut it still has to sound good: Zetex does!
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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)
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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
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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)
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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
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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
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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
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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
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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
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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
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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:
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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)
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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
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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
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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:
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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:
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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
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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
Output bridge Filter
Audio input
Gate driver
+-
DC Servo
AC comp network
Feedback circuits
Bridge supply
Input buffering and bias
Mute
ZXCD1210 modulator
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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:
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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
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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
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ZXCDSUBEV Series
Design flexibility:
PWMoutput
ZXCD1210 modulator
Output bridge Filter
Audio input
Gate driver
+-
DC Servo
AC comp network
Feedback circuits
Input buffering and bias
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
Output bridge Filter
Audio input
Gate driver
+-
DC Servo
AC comp network
Feedback circuits
Input buffering and bias
Mute
Protection options:Short circuit, thermal, DC
Bridge options:BTL & SE
Front end options: Volume, phase, filtering
PSU options:Regulated, Unregulated, linear, switching
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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
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