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IS31AP2005-SLS2-TR Datasheet(PDF) 11 Page - Integrated Silicon Solution, Inc |
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IS31AP2005-SLS2-TR Datasheet(HTML) 11 Page - Integrated Silicon Solution, Inc |
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11 / 19 page  IS31AP2005 Integrated Silicon Solution, Inc. – www.issi.com 11 Rev. C, 08/31/2015 INPUT CAPACITORS (CIN) The input capacitors and input resistors form a high-pass filter with the corner frequency, fC, determined in Equation (2). IN IN C R c f 2 1 (2) The value of the input capacitor is important to consider as it directly affects the bass (low frequency) performance of the circuit. Speakers in wireless phones cannot usually respond well to low frequencies, so the corner frequency can be set to block low frequencies in this application. Equation (3) is reconfigured to solve for the input coupling capacitance. C IN f R IN C 2 1 (3) If the corner frequency is within the audio band, the capacitors should have a tolerance of ±10% or better, because any mismatch in capacitance causes an impedance mismatch at the corner frequency and below. For a flat low-frequency response, use large input coupling capacitors (1μF). However, in a GSM phone the ground signal is fluctuating at 217Hz, but the signal from the codec does not have the same 217Hz fluctuation. The difference between the two signals is amplified, sent to the speaker, and heard as a 217Hz hum. SUMMING INPUT SIGNALS Most wireless phones or PDAs need to sum signals at the audio power amplifier or just have two signal sources that need separate gain. The IS31AP2005 makes it easy to sum signals or use separate signal sources with different gains. Many phones now use the same speaker for the earpiece and ringer, where the wireless phone would require a much lower gain for the phone earpiece than for the ringer. PDAs and phones that have stereo headphones require summing of the right and left channels to output the stereo signal to the mono speaker. SUMMING TWO DIFFERENTIAL INPUT SIGNALS Two extra resistors are needed for summing differential signals (Figure 14). The gain for each input source can be set independently by Equations (4) and (5). 1 1 150 2 1 IN IN O R k Gain V V V V (4) 2 2 150 2 2 IN IN O R k Gain V V V V (5) Figure 14 Application Circuit with Summing Two Differential Inputs If summing left and right inputs with a gain of 1V/V, use RIN1 = RIN2 = 300kΩ. If summing a ring tone and a phone signal, set the ring-tone gain to Gain2 = 2V/V, and the phone gain to Gain1 = 0.1V/V. The resistor values would be. RIN1 = 3MΩ, and RIN2 = 150kΩ. SUMMING A DIFFERENTIAL INPUT SIGNAL AND A SINGLE-ENDED INPUT SIGNAL Figure 15 shows how to sum a differential input signal and a single-ended input signal. Ground noise may couple in through IN- with this method. It is better to use differential inputs. The corner frequency of the single-ended input is set by CIN2, shown in Equation (6). To assure that each input is balanced, the single-ended input must be driven by a low-impedance source even if the input is not in use. The gain for each input source can be set independently by Equations (4) and (5). 2 2 2 2 1 C IN IN f R C (6) If summing a ring tone and phone signals, the phone signals should use the differential inputs while the ring tone should use the single-ended input. The phone gain is set at Gain1 = 0.1V/V, and the ring-tone gain is set to Gain2 = 2V/V, the resistor values would be RIN1 = 3MΩ, and RIN2 = 150kΩ. The high pass corner frequency of the single-ended input is set by CIN2. If the desired corner frequency is less than 20Hz. Hz k IN C 20 150 2 1 2 (7) pF C IN 53 2 (8) |
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