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ML33111 Datasheet(PDF) 11 Page - LANSDALE Semiconductor Inc. |
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ML33111 Datasheet(HTML) 11 Page - LANSDALE Semiconductor Inc. |
11 / 12 page www.lansdale.com Page 11 of 12 Issue A LANSDALE Semiconductor, Inc. ML33111 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. 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. Legacy Applications Information DEFINITIONS |
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