BA3880AS Rohm, BA3880AS Datasheet - Page 5

• Manufacturer Part Number: BA3880AS
• Description: High-definition sound processor
• Manufacturer: Rohm

BA3880AS / BA3880AFS
Audio ICs
! ! ! ! Circuit operation
The BA3880AS and BA3880AFS high-definition sound processor system ICs treat the amplifiers and speakers as a total
audio systems, and perform signal processing at the amplifier input stage to accurately reproduce the rise sections of
audio signals that determine the characteristics of sound, and ensure that the replayed audio is as close to the original
sound and as natural sounding as possible.
Problems relating to playback of sound on audio systems.
With naturally-generated sound, high-frequency harmonic components generally occur first, followed by the fundamental
frequency components. This also applies to the attack section of the sound that characterizes many musical instruments.
It is the amplitude component that gives form to the frequency component and envelope at the rising point of sound, and
this expresses the characteristics of the sound. Therefore, when replaying audio on audio playback systems, it is
extremely important that the rise section of the signal be expressed accurately with respect to the original sound.
However, there is inevitable mismatching between the speakers and amplifiers in current audio systems. Solid-state
power amplifiers use negative feedback techniques and operate off a fixed voltage supply, but as speakers are a current
element, mismatching in the system inevitably occurs. In addition, the speaker impedance characteristics are strongly
influenced by the electrical reactance of the voice coil, and the mechanical reactance of the cone assembly. As a result of
this, distortion is generated in the rising sections of audio signals, causing phase shift in the reproduced sound. In addition,
impedance increases in the treble region which reduces the speaker amplitude and reduces the harmonic component,
and as a result there is a tendency to masking of large mid-frequency signal components that follow, and this makes it
difficult to reproduce the rising sections of the sound.
! ! ! ! Operating principle
To solve the problems described above, the BA3880AS and BA3880AFS perform the audio signal processing described
below.
Phase shift compensation
BASS
MIDDLE
TREBLE
20
150
2.4k
20k
f (Hz)
The input signal is separated into three regions: bass (20Hz to 150Hz), middle (150Hz to 2.4kHz) and treble (2.4kHz to
20kHz). These regions are then joined again with the middle and treble regions phase shifted −180° and −360°
respectively with respect to the bass signal. This phase shift adjusts the delay time characteristic for each band and
minimizes the distortion of the rising section of the audio signal.
Amplitude compensation (harmonic compensation)
To maintain appropriate auditory balance for the treble region that is made up of harmonic components, a high-speed
detector and high-performance VCA circuit are used for amplitude control of the treble component. The amount of
compensation is determined from a calculation performed based on the DC level input to the CTL pin, and the DC level
detected from the input signal. The internal control signal obtained from this calculation compensates the amplitude of the
treble component input to the VCA. This amplitude compensation recovers the harmonic component, and improves the
reproduction clarity (definition level) of instruments and vocals.