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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： | 10/16頁 |
| 文件大小： | 359K |
| 代理商： | MC34115DW |
MC34115
CIRCUIT DESCRIPTION
10
MOTOROLA ANALOG IC DEVICE DATA
The continuously variable slope delta modulator (CVSD)
is a simple alternative to more complex conventional
conversion techniques in systems requiring digital
communication of analog signals. The human voice is
analog, but digital transmission of any signal over great
distance is attractive. Signal/noise ratios do not vary with
distance in digital transmission and multiplexing, switching
and repeating hardware is more economical and easier to
design. However, instrumentation A–D converters do not
meet the communications requirements. The CVSD A–D is
well suited to the requirements of digital communications and
is an economically efficient means of digitizing analog inputs
for transmission.
The Delta Modulator
The innermost control loop of a CVSD converter is a
simple delta modulator. A block diagram CVSD Encoder is
shown in Figure 11. A delta modulator consists of a
comparator in the forward path and an integrator in the
feedback path of a simple control loop. The inputs to the
comparator are the input analog signal and the integrator
output. The comparator output reflects the sign of the
difference between the input voltage and the integrator
output. That sign bit is the digital output and also controls the
direction of ramp in the integrator. The comparator is
normally clocked so as to produce a synchronous and
band–limited digital bit stream.
If the clocked serial bit stream is transmitted, received,
and delivered to a similar integrator at a remote point, the
remote integrator output is a copy of the transmitting control
loop integrator output. To the extent that the integrator at the
transmitting locations tracks the input signal, the remote
receiver reproduces the input signal. Low pass filtering at
the receiver output will eliminate most of the quantizing
noise, if the clock rate of the bit stream is an octave or more
above the bandwidth of the input signal. Voice bandwidth is
4.0 kHz and clock rates from 8.0 k and up are possible.
Thus, the delta modulator digitizes and transmits the analog
input to a remote receiver. The serial, unframed nature of
the data is ideal for communications networks. With no
input at the transmitter, a continuous one zero alternation is
transmitted. If the two integrators are made leaky, then
during any loss of contact the receiver output decays to
zero and receive restart begins without framing when the
receiver reacquires. Similarly, a delta modulator is tolerant
of sporadic bit errors. Figure 12 shows the delta modulator
waveforms while Figure 13 shows the corresponding CVSD
decoder block diagram.
The Companding Algorithm
The fundamental advantages of the delta modulator are its
simplicity and the serial format of its output. Its limitations are
its ability to accurately convert the input within a limited digital
bit rate. The analog input must be band limited and amplitude
limited. The frequency limitations are governed by the
nyquist rate while the amplitude capabilities are set by the
gain of the integrator.
The frequency limits are bounded on the upper end; that
is, for any input bandwidth there exists a clock frequency
larger than that bandwidth which will transmit the signal with
a specific noise level. However, the amplitude limits are
bounded on both upper and lower ends. For a signal level,
one specific gain will achieve an optimum noise level.
Unfortunately, the basic delta modulator has a small dynamic
range over which the noise level is constant.
The continuously variable slope circuitry provides
increased dynamic range by adjusting the gain of the
integrator. For a given clock frequency and input bandwidth
the additional circuitry increases the delta modulator’s
dynamic range. External to the basic delta modulator is an
algorithm which monitors the past few outputs of the delta
modulator in a simple shift register. The register is 3–bits
long. The accepted CVSD algorithm simply monitors the
contents of the shift register and indicates if it contains all 1s
or 0s. This condition is called coincidence. When it occurs, it
indicates that the gain of the integrator is too small. The
coincidence output charges a single–pole low pass filter. The
voltage output of this syllabic filter controls the integrator gain
through a pulse amplitude modulator whose other input is the
sign bit or up/down control.
The simplicity of the all 1s, all 0s algorithm should not be
taken lightly. Many other control algorithms using the shift
register have been tried. The key to the accepted algorithm is
that it provides a measure of the average power or level of
the input signal. Other techniques provide more
instantaneous information about the shape of the input curve.
The purpose of the algorithm is to control the gain of the
integrator and to increase the dynamic range. Thus, a
measure of the average input level is what is needed.
The algorithm is repeated in the receiver and thus the level
data is recovered in the receiver. Because the algorithm
operates only on the past serial data, it changes the nature of
the bit stream without changing the channel bit rate.
The effect of the algorithm is to compand the input signal.
If a CVSD encoder is played into a basic delta modulator, the
output of the delta modulator will reflect the shape of the input
signal but all of the output will be at an equal level. Thus, the
algorithm at the output is needed to restore the level
variations. The bit stream in the channel is as if it were from
a standard delta modulator with a constant level input.
The delta modulator encoder with the CVSD algorithm
provides an efficient method for digitizing a voice input in a
manner which is especially convenient for digital
communications requirements.
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相關代理商/技術參數 |
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| 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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