MC33111D 데이터 시트보기 (PDF) - Motorola => Freescale
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MC33111D Datasheet PDF : 12 Pages
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The MC33111 compander is not limited to RF or long
distance telephony applications. It can be used in any system
requiring either an improved signal-to-noise ratio, or a reduced
dynamic range. Such applications include telephones,
speakerphones, tape recorders, wireless microphones, digital
recording, and many others.
Power Supplies, Grounding
The PC board layout, and the quality of the power supplies
and the ground system at the IC are very important in order
to obtain proper operation. Noise, from any source, coming
into the device on VCC or ground, can cause a distorted
output, or incorrect gain levels.
VCC must be decoupled to the appropriate ground at the IC
(within 1″ max.) with a 4.7 µF capacitor and a 0.01 µF ceramic.
A tantalum capacitor is recommended for the larger value if
very high frequency noise is present, since electrolytic
capacitors simply have too much inductance at those
frequencies. The quality of the power supply voltage should be
checked at the IC with a high frequency scope. Noise spikes
(always present if digital circuits are near this IC) can easily
exceed 400 mV, and if they get into the IC, the output can have
noise or distortion. Noise can be reduced by inserting resistors
and/or inductors between the supply and the IC.
If switching power supplies are used, there will be spikes
of 0.5 V or greater at frequencies of 50 kHz – 1.0 MHz. These
spikes are generally more difficult to reduce because of their
greater energy content. In extreme cases, a 3-terminal
regulator (e.g., MC78L05ACP), with appropriate high
frequency filtering, should be used and dedicated to the
analog portion of the circuit.
The ripple content of the supply should not allow its
magnitude to exceed the values in the Recommended
Operating Conditions table.
The PC board tracks supplying VCC and ground to the
MC33111 should preferably not be at the tail end of the bus
distribution, after passing through a maze of digital circuitry.
The analog circuitry containing the MC33111 should be close
to the power supply, or the connector where the supply
voltages enter the board. If VCC is supplying considerable
current to other parts of the board, then it is preferable to
have dedicated lines directly to the MC33111 and associated
circuitry.
PC Board Layout
Although this device is intended for use in the audio
frequency range, the various amplifiers have a bandwidth of
≈ 300 kHz, and can therefore oscillate at frequencies outside
the voiceband should there be excessive stray capacitance
or other unintended feedback loops. A solid ground plane is
strongly recommended to minimize coupling of any digital
noise into the analog section. Use of wire wrapped boards
should definitely be avoided.
Since many applications of the MC33111 compander
involve voice transmission over RF links, care must be taken
in the design of the product to keep RF signals out of the
MC33111 and associated circuitry. This involves proper
layout of the PC boards and the physical arrangement of the
boards, shielding, proper RF ground, etc.
DEFINITIONS
Attack Time — The settling time for a circuit after its input
signal has been increased.
Attenuation — A decrease in magnitude of a
communication signal, usually expressed in dB.
Bandwidth — The range of information carrying
frequencies of a communication system.
Channel Separation — The ability of one circuit to reject
outputting signals which are being processed by another
circuit. Also referred to as crosstalk rejection, it is usually
expressed in dB.
Compander — A contraction of the words compressor
and expander. A compander is composed of two circuits, one
of each kind.
Compressor — A circuit which compresses, or reduces,
the dynamic range of a signal by attenuating strong signals
and amplifying low level signals.
dB — A power or voltage measurement unit, referred to
another power or voltage. It is generally computed as:
10 x log (P1/P2) for power signals, and
20 x log (V1/V2) for voltage signals.
dBm — An indication of signal power. 1.0 mW across 600 Ω,
or 0.775 Vrms, is typically defined as 0 dBm for telecom
applications. Any voltage level is converted to dBm by:
dBm = 20 x log (Vrms/0.775), or
dBm = [20 x log (Vrms)] + 2.22.
dBrn — Indicates a dBm measurement relative to 1.0 pW
power level into 600 Ω. Generally used for noise measure-
ments, 0 dBm = – 90 dBm.
dBrnC — Indicates a dBrn measurement using a
C-message weighting filter.
Decay Time — The settling time for a circuit after its input
signal has been decreased.
Expander — A circuit which expands, or increases the
dynamic range of a signal by amplifying strong signals and
attenuating low level signals.
Gain — The change in signal amplitude (increase or
decrease) after passing through an amplifier, or other circuit
stage. Usually expressed in dB, an increase is a positive
number, and a decrease is a negative number.
Mute — Reducing the level of an audio signal, generally
so that it is inaudible. Partial muting is used in some
applications.
Passthrough — Bypassing the compression and/or
expansion function by setting the gain to a fixed value
(usually unity). This is usually employed when data, rather
than voice, is to be transmitted without attenuation.
Power Supply Rejection Ratio — The ability of a circuit
to reject outputting noise, or ripple, which is present on the
power supply lines. PSRR is usually expressed in dB.
Signal to Noise Ratio — The ratio of the desired signal to
unwanted signals (noise) within a defined frequency range.
The larger the number, the better.
Voiceband — That portion of the audio frequency range
used for transmission in the telephone system. Typically it is
300-3400 Hz.
Zero dB Point — The signal level which has its amplitude
unchanged by a compressor or expander.
MC33111
MOTOROLA
11
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