The BA1604 and BA1604F are tone decoder ICs that enable the frequency to be selected in precise detail, using a PLL system. These ICs are configured of a PLL circuit, a detection circuit, a voltage comparator circuit and an output logic drive circuit.
When the input signal is within the transmission range of the circuit, PLL is synchronized (locked) to the input signal. At this point, the output voltage of the decoder drops, and the change turns on the transistors for the voltage comparator and output logic drive circuits. A load of up to 100mA can be driven.The center frequency (f0) of the decoder is set by the mobile oscillation frequency of the current control oscillator. This frequency is determined by selecting a CR connected to Pins 5 and 6.

Features
1) The detection bandwidth can be varied independently between 0 and 14%.
2) The output circuit can withstand a load current of up to 100mA, and is directly coupled to the logic circuit.
3) The center frequency offers a high level of stability.
4) High out-of-band signal and noise rejection capability.
5) Frequency can be changed over a range of 20 : 1 using an external resistor.
6) Compatible with EXAR XR-567 and Signetics NE567.

Applications
    Telephones
    Data communication systems
    Remote control systems