Sharp SM-SX100 Service Manual page 16

SM-SX100
3. Application to amplifying circuit: 1-bit amplifier
3-1) Basic block and operational principle
The system classified as "Class C amplifier" among the amplification circuits switches the high voltage to control the ON
time in order to amplify the audio signal.
"PWM signal" which has the analog width in the time axis direction is generally used as the signal to control the switching.
The operational principle of Class D amplifier is developed to apply the said 7th order
signal which controls the signal. Thus, the 1-bit amplifier "SM-SX100" is introduced.
Line 1 (RCA PIN)
Line 2 (Canon)
Analog Signal
Input
SACD (Analog)
SACD (1bit)
1-Bit Signal Input
Digital 1(ST LINK)
Digital 2(RNC)
Digital
Multi-Bit Signal
Interface
Input Terminal
Circuit
Digital 3(RCA)
Digital 4(TOS LINK)
Digital 1 Digital 2 Digital 3 Digital 4 SACD Analog 1
Function Switch
Digital 1 Digital 2 Digital 3 Digital 4 SACD Analog 1 Analog 2
Function Indicator
Fig. 16 shows the basic block of the 1-bit amplifier. In the block diagram, the core of the amplifying operation is "1-bit
amplification signal process circuit", being composed of the following four circuits. 1
2 7th order modulation 1-bit signal generation circuit
3 Digital driver circuit
4 Power switching circuit
Low pass filter circuit 1
In the circuit , the input signal is processed through the high-speed sampling
signal array" which is directly coded from the input information. (Said 7th order
Though the 1-bit signal is used as the control signal to switch the constant-voltage power supply at the timing of the quartz
precision, the digital driver circuit 3
switching circuit composed of Power MOS-FET is operated at the high speed.
Though the constant voltage is supplied to the power switching circuit
and the error component of the power switching are included in the output section of
feedback" loop which negatively feeds the information of the output section back to "7th order 1
generation circuit " at the high speed is provided to compensate the above fluctuation noise and error component at the
real time. The feedback operation achieves "power amplification faithful to input signal" without influence of the power
fluctuation and so on.
Since the 1-bit signal of 64fs originally catches the analog signal at the sampling frequency of 64 x 44.1 kHz = 2.8224 MHz,
the information can be transferred to the band of approx. 1.4 MHz, a half of the sampling frequency as the principle.
In the practical circuit, the band is limited at 100 kHz as the result of the following being considered to determine the pass
band.
1) The quantized noise of the 1-bit signal increases toward the high range, and it eliminates the band where the quantized
noise increases in the high range.
2) If any high frequency component of 100 kHz or more is included in the analog signal when an analog signal is taken out
of the 1-bit signal, an abnormality will occur in the circuit system and transfer system of the following step. (Example:
High frequency oscillation, unnecessary radiation, tweeter breakage, etc.)
3) The frequency component of the acoustic signal which is present in the natural is distributed in the band up to 100 kHz.
In the low pass filter circuit
for which the voltage is converted, and are output as the analog signal for the speaker drive.
Volume
Control
Analog Signal
1-Bit Signal
Volume Indicator
Sampling Rate Circuit of 1-Bit
Converter Conversion
Circuit
From Multi-Bits
LED Driver Circuit
Analog 2
LED Driver Circuit
Figure 16 1-BIT AMP. SM-SX100 BLOCK DIAGRAM
2
controls the drive, suppressing the delay to the minimum since the full bridge power
4
of the last step, the components up to 100 kHz are taken out from the the switching signal
1-Bit Amplification Signal Process Circuit
Power Switching
7th Order
Circuit
∆∑ Modulation
Digital Driver
1-Bit Signal
Circuit
Generation Circuit
∆∑ Dynamic Feedback
–22V
DC Power
Supply Circuit
+5V +5V +12V –12V
Control
DC Power
Microcomputer
Supply Circuit
+5V
3
, the fluctuation noise included in the power supply
– 16 –
modulation 1-bit signal to the
Bi-wiring Speaker
Terminal
Low-Pas Filter
Circuit
Power
Fuse Switch
+32V
Switching
–32V
Power Circuit
modulation circuit to generate "1-bit
modulation LSI)
3
. Therefore, the " dynamic
modulation 1-bit signal
Speaker