Internal circuit and application circuit of BA3884 (a)

The DC operating voltage of BA3884 is 5.4~12.3V. Its internal circuit principle and application circuit are shown in Figure 5-16.
This circuit is a two-channel processing circuit, containing two sets of identical processing circuits. It can complete the following audio signal processing.
    Phase compensation. The audio signal is input into the two channels of the LC through pin 14.23, and is divided by the low-pass filter LPF, the band-pass filter BPF, and the high-pass filter HPF into three
channels: 20-150Hz, 150Hz~2.4kHz and 2.4kHz~20kHz The frequency bands are processed separately, and finally the processed signals are added and synthesized and output from pins 13 and 24 respectively. Since the fundamental wave of sound is located in the mid-frequency band and the higher harmonics are located in the high-frequency band, in order to eliminate the phase distortion caused by high delay, this circuit adopts a fixed high frequency, so that the mid-range band lags behind the high-frequency band by 1 80. , the bass band lags behind the treble band by 3600. Due to the hysteresis processing of the mid-range and bass bands , the delay phenomenon of the high-frequency bands is exactly compensated and corrected, and the phase distortion is eliminated.     Amplitude compensation (harmonic compensation) o In order to compensate for the speaker's insufficient amplitude response to high-frequency harmonics, the high-speed peak detector and voltage-controlled amplifier VCA automatically control the amplitude of high-frequency harmonics as needed. Correction and compensation are controlled by two DC voltages. One DC voltage is provided by an external voltage divider circuit and is added to the CTL ① terminal; the other DC voltage is obtained by detecting the input signal by the peak detector, and is added by the high-frequency harmonics of the HPF. To the VCA input end, compensation correction is completed by a special circuit. After amplitude correction, the harmonics reflecting the subtle characteristics of the sound are restored and strengthened, allowing the playback system to produce high- resolution, high-definition and natural-sounding sounds. The DC voltage applied to the CTL1 terminal is adjusted by the base)2 of the voltage divider circuit. When it is turned on When switch K is placed in the "ON" position, it is the BBE working state. When the voltage of pin 8 of CTL1 changes from 4.5V-Oy, the resolution and clarity of the audio signal processed by IX     are improved by OdB9, 5dBo bass contour. To restore the phase and amplitude of high-order harmonics, appropriate bass is needed to achieve the best balance. The processing system uses a bass contour boost circuit to achieve the most ideal linear boost from the range of 50 N150Hz. The boost circuit is improved by Adjusted by the voltage divider circuit RPi, when the DC voltage at pin 7 of rL2 changes from 4.5V to OV, the bass boost amount increases from OdB+8.7dB. Through the bass boost, the entire sound playback system achieves balanced high and low sound playback.