MCD stands for "MHz Class-D", A
new amplifier technology from John.Fu(Fumac)
and Zhaolian.Fu. This New Class D amplifier
technology runs a very high sampling rate
Frequency (from around 700KHz~2.6Mhz, at
a fixed frequency). This technology enables
us to produce amplifiers of high power(up
to 800w), Low THD(0.00x%), Low phase-shift,
and a Class A like sound all from a compact,
cool running, environmentally friendly design,
perfect for a HiFi, AV system, active speaker
or professional amplifier.
MCD amplifiers feature two feedback paths
(Figure 1), one to produce the High Frequency
oscillation frequency, the other for AF error
feedback, this AF feedback includes the output
filter to ensure load independent performance.
By combining these two loops, you can create
a system with both outstanding technical
and subjective performance.
AF Error Feelback , Low THD
MCD has an AF error feedback from the speaker
terminal , this feedback can fix the large
THD from the filter , so MCD can get a very
low THD also at very high power output. Figure
5: samples of THD in high power output .
THD spectrum analyzer of MCD-300 at 2W 6ohm,
THD=0.0035%(-87db) at 1k ,THD=0.0100%(-80db)
at 7k ,THD=0.0112%(-79db) at 15k
THD spectrum analyzer of MCD-300 at 100W(rms)
6ohm,
THD=0.016%(-76db) at 100Hz ,THD=0.012%(-78db)
at 1k ,THD=0.016%(-74.5db) at 7k
The Higher The Sample Frequency , The More
Detail
Previous Class D technology ran below 100KHz.
This is not quick enough for full-range (10Hz~20KHz)
audio performance, and can only be consider
suitable for subwoofer (10Hz to 250Hz) applications.
More recently Class D designers have been
able to increase the switching frequency
of their designs to 200k~250k. These type
of Class D amplifiers can produce close to
full range audio (about 10hz ~18KHz). Typically
these designs had great bass but poor treble.
Still these amplifiers have found homes in
AV systems, sub woofers, and Mid Fi applications.
Figure 2 show level error at different speed
of damp.
Bringing us up to date, there are some very
good designs that now run at between 350¨C400KHz.
These are the first designs that can reproduce
the accepted "full bandwidth" (10Hz~22kHz)
with finesse . However, the phase shift between
bass and treble is to great to produce a
fully cohesive sound. (Figure 3)..
High Frequency, Low Phase-shift, Low EMI
MCD runs at speeds of between 700KHz to 2.6MHz
(up to 6 times faster then the current state
of the art), It has an extended audio bandwidth
from below 1Hz to beyond 60KHz with a simple
filter (80KHz Low Pass Filter), as the high
switching speed makes this possible.
Looking at he picture(Figure 3 and Figure
4), the MCD generates lower EMI, has less
phase shift and has a greater bandwidth than
other D Class amplifiers. With a AF error
feedback, the phase shift can be zero.
Balance response
A Butterworth filter is inside most of HIFI
class-d amps, this is make the lowest EMI
of damp, make it work well with others.
Some old class-d amp have a 3V carrier frequency
output(about 280mW, like a ).Class-d amp
running in 400k have 0.8V(about 20mW to 4ohm,
like the output power of wireless microphone)
. Through the speaker line, it will transmit
to anywhere. MCD just have less than 0.1V(about
0.3mW ) carrier frequency output. It's very
lower than the others.
A simple filter can't make the balance with
audio frequency flag , low phase shift and
lowest carrier frequency output, except the
carrier frequency far away from the audioband.
But MCD can, because the very high frequency(700k~2.65MHz).(Figure
3 Figure 4 )
Active loads
Speakers have different loads, a 4ohm speaker
some times between 2ohm to 8ohm, sometimes
we use a same AMP to drive different speakers,
this is call active load character.
The simple filter of class-d amp response
like Figure 5 , we found that the treble
will different in the different load.
Figure 6 shows the active load character
include 400k class-d amp and MCD, we found
that the MCD have a more flag response than
the 400K class-d amp (13.7dB VS 7.5dB from
1ohm to 16ohm) . This is meaning MCD can
driver different load with a same-like response.
MCD with a very strong current output, most
types of MCD can driver 1ohm load.
15 Years Experience, offer customs design
John.Fu and ChaoLian.Fu are the designer
of MCD . They have Experience working in
RF design and AF design for 15 years, Good
at super high speed PCB design and Hi-FI
audio design. This make the MCD work in very
high performance. We offer our designs to
other companies for Custom design all around
the world.
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copy right: john.fu zhaolian.fu 2006~2007
email: fumac1@gmail.com (skype)
website: www.class-d.net