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ML33111 Datasheet PDF : 12 Pages
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ML33111
LANSDALE Semiconductor, Inc.
Legacy Applications Information
The ML33111 compander is not limited to RF or long dis-
tance 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 tele-
phones, 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 out-
put, 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 electrolyt-
ic capacitors simply have too much inductance at those fre-
quencies. 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 fre-
quency 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
ML33111 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 ML33111 should be close
to the power supply, or the connector where the supply volt-
ages enter the board. If VCC is supplying considerable current
to other parts of the board, then it is preferable to have dedi-
cated lines directly to the ML33111 and associated circuitry.
PC Board Layout
Although this device is intended for use in the audio fre-
quency 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 ML33111 compander
involve voice transmission over RF links, care must be taken
in the design of the product to keep RF signals out of the
ML33111 and associated circuitry. This involves proper lay-
out 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 sig-
nal, usually expressed in dB.
Bandwidth — The range of information carrying frequencies of a
communication system.
Channel Separation — The ability of one circuit to reject out-
putting 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 amplify-
ing 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 measurements, 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 func-
tion by setting the gain to a fixed value (usually unity). This is usual-
ly employed when data, rather than voice, is to be transmitted with-
out 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 unwant-
ed 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.
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