SD-EX220H
5 – 2
[3] Description of circuit for 1-bit unit (See the wiring diagrams on pages 6-16 and 6-17)
Input section
Signals from CNA101 are coupled by CA100 and CA101 and then sent
into the A/D converter IC (ICA100).
∆Σ
modulation 1-bit converter
Signals from the A/D converter IC (ICA100) are converted to 1-bit sig-
nals and sent differentially. Refer to the technical manual of SM-SX100
for the details of conversion to 1-bit signals.
Low pass filter circuit
1-bit signals switched by the output IC (ICA101 and ICA102) are con-
verted to analog signals through the lowpass filter consisting of LA101
~ LA107. The low pass filter functions when a frequency exceeds 20
kHz, and reduces it by approx. 3 dB when it reaches approx. 40 kHz.
Dynamic feedback circuit
The 1-bit signals switched by the output IC (ICA101 and ICA102) oscil-
late between positive and negative voltage. After resistance-division,
the signals are fed back to the A/D converter IC (ICA100) through NF
resistance 75 kohms (RA155 ~ RA158). The peak-to-peak voltage
reaches approx. 5 V.
[4] Waveforms of 1-bit circuit
T
2
1
2.00V/div
500 ns/div
194.545465 µs
520 mV
2.00V/div
AD IC Output
+ Side
- Side
5 V
Amplitude
from 0 to 5 V
1
2
2
1
2.00 V/div
500 ns/div
194.545465 µs
-12.30 V
2.00 V/div
AD IC NF IN
In partial pressure OUT, 4 to 7 V amplitude
of GND reference is observed.
In IC of 75 kohms, the reference is 2.5 V
because of VREF. Due to imaginary GND
of operational amplifier inside IC, the
waveform cannot be monitored.
This waveform is partial pressure OUT.
3
4
T
2.00 V/div
50.0 ns/div
0.0 s
-12.30 V
2.00 V/div
LEVEL SHIFT OUT
DEAD TIME
ZOOM UP
Dead time is generated by level
shift input.
Leading edge is delayed at CR,
passing R at DI.
Set value: 20 - 25 nsec.
5
6
T
10.0 V/div
500 ns/div
194.545465 µs
-12.3 V
10.0 V/div
+ SIDE
+ FETOUT
- SIDE
Waveforms before low-pass filters at both
ends of the speaker.
H-bridge may be considered as BTL.
However, here and at the gate drive, dead
time is not observed; since bootstrap
operates based on output, DEAD TIME
part is in floating condition. The waveform
on the HIGH side shows that only the
booted voltage lowers.
2
1
11
12
