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IS31AP2010B-UTLS2-TR Datasheet(PDF) 9 Page - Integrated Silicon Solution, Inc |
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IS31AP2010B-UTLS2-TR Datasheet(HTML) 9 Page - Integrated Silicon Solution, Inc |
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9 / 13 page  IS31AP2010B Integrated Silicon Solution, Inc. – www.issi.com Rev.B, 04/10/2013 9 APPLICATION INFORMATION FULLY DIFFERENTIAL AMPLIFIER The IS31AP2010B is a fully differential amplifier with differential inputs and outputs. The fully differential amplifier consists of a differential amplifier and a common mode amplifier. The differential amplifier ensures that the amplifier outputs a differential voltage on the output that is equal to the differential input times the gain. The common-mode feedback ensures that the common-mode voltage at the output is biased around VCC/2 regardless of the common-mode voltage at the input. The fully differential IS31AP2010B can still be used with a single-ended input; however, the IS31AP2010B should be used with differential inputs when in a noisy environment, like a wireless handset, to ensure maximum noise rejection. ADVANTAGES OF FULLY DIFFERENTIAL AMPLIFIERS The fully differential amplifier does not require a bypass capacitor. This is because any shift in the mid-supply affects both positive and negative channels equally and cancels at the differential output. GSM handsets save power by turning on and shutting off the RF transmitter at a rate of 217Hz. The transmitted signal is picked-up on input and output traces. The fully differential amplifier cancels the signal much better than the typical audio amplifier. COMPONENT SELECTION Figure 10 shows the IS31AP2010B with differential inputs and input capacitors, and Figure 11 shows the IS31AP2010B with single-ended inputs. Differential inputs should be used whenever possible because the single-ended inputs are much more susceptible to noise. OUT+ GND IS31AP2010B B1,B2 A3 C3 VCC OUT- CS 1 F VBattery C1 IN- IN+ A1 0.1 F A2,B3 SDB C2 100k CIN+ 0.1 F CIN- 0.1 F RIN+ 150k RIN- 150k Differential Input Shutdown Control Figure 10 Differential Input Figure 11 Single-Ended Input INPUT RESISTORS (RIN) The input resistors (RIN) set the gain of the amplifier according to Equation (1). IN F R R ain 2 G V V (1) Resistor matching is very important in fully differential amplifiers. The balance of the output on the reference voltage depends on matched ratios of the resistors. CMRR, PSRR, and cancellation of the second harmonic distortion diminish if resistor mismatch occurs. Therefore, it is recommended to use 1% tolerance resistors or better to keep the performance optimized. Matching is more important than overall tolerance. Resistor arrays with 1% matching can be used with a tolerance greater than 1%. Place the input resistors very close to the IS31AP2010B to limit noise injection on the high-impedance nodes. For optimal performance the gain should be set to 2V/V or lower. Lower gain allows the IS31AP2010B to operate at its best, and keeps a high voltage at the input making the inputs less susceptible to noise. DECOUPLING CAPACITOR (CS) The IS31AP2010B is a high performance Class-D audio amplifier that requires adequate power supply decoupling to ensure the efficiency is high and total harmonic distortion (THD) is low. For higher frequency transients, spikes, or digital hash on the line, a good low equivalent-series-resistance (ESR) ceramic capacitor, typically 1μF, placed as close as possible to the device VCC lead works best. Placing this decoupling capacitor close to the IS31AP2010B is very important for the efficiency of the Class-D amplifier, because any resistance or inductance in the trace between the device and the capacitor can cause a loss in efficiency. For filtering lower frequency noise signals, a 10μF or greater capacitor placed near the audio power amplifier would also help, but it is not required in most applications because of the high PSRR of this device. |
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Similar Description - IS31AP2010B-UTLS2-TR |
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