전자부품 데이터시트 검색엔진 |
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BA3121 데이터시트(PDF) 5 Page - Rohm |
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BA3121 데이터시트(HTML) 5 Page - Rohm |
5 / 11 page Vi = R4 (R3 )R4) S e2 eO = * R1 )R2 R1 S Vi R2 R1 e1 ) eO = * R1 )R2 R1 S e2 R2 R1 e1 ) eO = * R1R4 *R2R3 R1 (R3 )R4) S e2 R2 R1 S (e1*e2) ) R4 (R3 )R4) S 1 2 721 Audio ICs BA3121 / BA3121F / BA3121N FCircuit operation Car-audio systems are earthed to the car body, and for this reason, electrical noise generated by the car elec- trics can enter the power amplifier input via the chassis, and become audible. The BA3121 makes use of the common-mode rejection characteristics of an operational amplifier to eliminate this noise. Without the BA3121 noise enters the power amplifier input directly, when used, the CMMR of opera- tional amplifiers 1-A and 2-A eliminates the noise. Principles of noise elimination: To obtain the output voltage (eO) From 1 and 2 Ideally, if R1R4 = R2R3, and e1 = e2, the noise voltage will become zero. However, due to mismatching between the resistors, difference in the noise voltages (e1 and e2), and tolerances in the operational amplifier, a noise voltage does result. With the BA3121, the elimination level of the noise is ex- pressed as: CMMR = 20log (eO /ei) (ei = e1 = e2) Therefore, CMRR y 41dB can be guaranteed. FOperation notes (1) Maintain a ratio of 2: 1 for the values of the capaci- tors connected to pin 2 (Vm1) and pin 6 (Vm2) to keep the ripple rejection ratio stable. If this ratio is maintained, the ripple rejection ratio will not vary significantly even if the capacitance values are halved. (2) If the value of the capacitor connected to pin 2 (Vm1) in the example is doubled, the bass-region CMMR will be +6dB, and if it is halved, it will be *6dB (see Fig. 16). |
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