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參數資料
| 型號： | MC34115DW |
| 廠商： | MOTOROLA INC |
| 元件分類： | 編解碼器 |
| 英文描述： | CONTINUOUSLY VARIABLE SLOPE DELTA MODULATOR/DEMODULATOR |
| 中文描述： | CVSD, CVSD CODEC, PDSO16 |
| 封裝： | PLASTIC, SO-16 |
| 文件頁數： | 13/16頁 |
| 文件大小： | 359K |
| 代理商： | MC34115DW |
MC34115
13
MOTOROLA ANALOG IC DEVICE DATA
INCREASING CVSD PERFORMANCE
Integration Filter Design
The circuit in Figure 15 uses a single–pole integration
network formed with a 0.1
μ
F capacitor and a 10 k
resistor.
It is possible to improve the performance of the circuit in
Figure 15 by 1.0 or 2.0 dB by using a two–pole integration
network. The improved circuit is shown in Figure 17.
The first pole is still placed below 300 Hz to provide the 1/S
voice content curve and a second pole is placed somewhere
above the 1.0 kHz frequency. For telephony circuits, the
second pole can be placed above 1.8 kHz to exceed the
1633 touchtone frequency. In other communication systems,
values as low as 1.0 kHz may be selected. In general, the
lower in frequency the second pole is placed, the greater the
noise improvement. Then, to ensure the encoder loop
stability, a zero is added to keep the phase shift less than
180
°
. This zero should be placed slightly above the low–pass
output filter break frequency so as not to reduce the
effectiveness of the second pole. A network of 235 Hz,
2.0 kHz and 5.2 kHz is typical for telephone applications
while 160 Hz, 1.2 kHz and 2.8 kHz might be used in voice
only channels. (Voice only channels can use an output
low–pass filter which breaks at about 2.5 kHz.) The two–pole
network in Figure 17 has a transfer function of:
VO
Ii
R0R1 S
1
R1C1
R2C2(R0
R1)
S
1
R1 C1
R0
S
1
R2C2
Figure 17. Improved Filter Configuration
0.15
Analog
Output
C2
R1
13 k
600
C1
0.1
5
7
MC34115
NOTE:
These component values are for the telephone channel
circuit poles described in the text. The R2, C2 product can
be provided with different values of R and C. R2 should be
chosen to be equal to the termination resistor on Pin 1.
R0
600
R2
6
Thus, the two poles and the zero can be selected arbitrarily
as long as the zero is at a higher frequency than the first pole.
The values in Figure 17 represent one implementation of the
telephony filter requirement.
The selection of the two–pole filter network affects the
selection of the loop gain value and the minimum step size
resistor. The required integrator current for a given change in
voltage now becomes:
VO
R0
R0
R2C2C1
R1C1R2C2
R0
VO2
T2
Ii
R2C2
R1C1
R0
C1
VO
T
The calculation of desired gain resistor Rx then proceeds
exactly as previously described.
Syllabic Filter Design
The syllabic filter in Figure 15 is a simple single–pole
network of 18 k
and 0.33
μ
F. This produces a 6.0 ms time
constant for the averaging of the coincidence output signal.
The voltage across the capacitor determines the integrator
current which in turn establishes the step size. The integrator
current and the resulting step size determine the companding
ratio and the S/N performance. The companding ratio is
defined as the voltage across CS/VCC.
The S/N performance may be improved by modifying the
voltage to current transformation produced by Rx. If different
portions of the total Rx are shunted by diodes, the integrator
current can be other than (VCC – VS)/Rx. These breakpoint
curves must be designed experimentally for the particular
system application. In general, one would wish that the
current would double with input level. To design the desired
curve, supply current to Pin 4 of the codec from an external
source. Input a signal level and adjust the current until the
S/N performance is optimum. Then record the syllabic filter
voltage and the current. Repeat this for all desired signal
levels. Then derive the resistor diode network which
produces that curve on a curve tracer.
Once the network is designed with the curve tracer, it is
then inserted in place of Rx in the circuit and the forced
optimum noise performance will be achieved from the active
syllabic algorithm.
Diode breakpoint networks may be very simple or
moderately complex and can improve the usable dynamic
range of any codec. In the past they have been used in high
performance telephone codecs.
Typical resistor–diode networks are shown in Figure 18.
Figure 18. Resistor–Diode Networks
R1
R2
D1
R1
R2
D1
D2
D3
R3
Output Low Pass Filter
A low pass filter is required at the receiving circuit output to
eliminate quantizing noise. In general, the lower the bit rate,
the better the filter must be. The filter in Figure 19 provides
excellent performance for 12 kHz to 40 kHz systems.
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| MC34117D | ECONOLINE: RSZ/P - 1kVDC |
| MC34117 | Telephone tone ringer |
| MC34117P | Telephone tone ringer |
| MC34118 | ECONOLINE: RSZ/P - 1kVDC |
| MC34118DW | VOICE SWITCHED SPEAKERPHONE CIRCUIT |
相關代理商/技術參數 |
參數描述 |
|---|---|
| MC34115P | 制造商:MOTOROLA 制造商全稱:Motorola, Inc 功能描述:CONTINUOUSLY VARIABLE SLOPE DELTA MODULATOR/DEMODULATOR |
| MC34117 | 制造商:SPC Multicomp 功能描述:AXIAL FAN 17MM 3VDC 制造商:SPC Multicomp 功能描述:AXIAL FAN, 17MM, 3VDC 制造商:SPC Multicomp 功能描述:AXIAL FAN, 17MM, 3VDC; Frame Dimensions:17mm x 17mm x 3mm; Supply Voltage:3VDC; Current Rating:37mA; Flow Rate - Imperial:0.5cu.ft/min; Flow Rate - Metric:6.17l/min; Noise Rating:32.8dBA; Bearing Type:Vapo; Current Rating:39mA ;RoHS Compliant: Yes 制造商:SPC Multicomp 功能描述:AXIAL FAN, 17MM, 3VDC; Frame Dimensions:17mm x 17mm x 3mm; Supply Voltage:3VDC; Current Rating:37mA; Flow Rate - Imperial:0.5cu.ft/min; Flow Rate - Metric:6.17l/min; Noise Rating:32.8dBA; Bearing Type:Vapo; Series:-; Current Type:DC ;RoHS Compliant: Yes |
| MC34117D | 制造商:MOTOROLA 制造商全稱:Motorola, Inc 功能描述:Telephone tone ringer |
| MC34117P | 制造商:MOTOROLA 制造商全稱:Motorola, Inc 功能描述:Telephone tone ringer |
| MC34118 | 制造商:FREESCALE 制造商全稱:Freescale Semiconductor, Inc 功能描述:Specifications and Applications Information |
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