579

Audio ICs

BA3826S

(2)

Band-pass filter circuit

This circuit extracts the required frequency range from

the input signal and amplifies it.

The center frequency is determined by the value of the

current flowing through the resistor connected to pin 14.

Q is set to 3.5 (Typ.).

Due to the characteristics of the band-pass filter circuit,

the circuit has a transition rise and fall characteristic. Due

to the transition rise characteristic, five input cycles are

required until peak output is reached.

When RESET is input, a built-in circuit cancels the fall

transition characteristic (input the reset signal for 0.5ms).

(3)

DET circuit

The DET circuit detects the signal selected by the band

pass filter and performs peak hold.

The RESET Driver discharges the charge stored in the

capacitor. After the RESET input is released, the RESET

Driver discharges continuously for 14ms.

(4)

Timing

1) RESET timing

The RESET input is used as the RESET signal for the

band-pass filter circuit and the DET circuit. The setting

time is 0.5ms min.

When performing a RESET input, disable both the Lin

and Rin inputs. The synchronous shift in this case must

be

"0.1ms max.

2) Output select timing

The audio input signal is not accepted when the RESET

input and L (R) inputs are low. There are no particular re-

strictions on the select input for the various frequencies,

but there are delay times until the peak voltage is settles

(see (a) and (b) below). Accordingly, set the read timing

for the DET signal after the longer of the delay times in

(a) and (b).

(a)

For the band-pass filter, a sampling time of at least

5 cycles is required due to the transition rise characteris-

tic.