PASS FILTER. NJU7505A Datasheet
BAND PASS FILTER
FOR AUDIO SPECTRUM ANALYZER DISPLAY
The NJU7505A is a band pass filter for audio spectrum
It consists of high and low band pass filters, CR oscillation
circuit, control circuit and DC transfer circuit.
Each band pass filter using the switched capacitor filter
technology operates at the shared time by 5 bands which
filter constant is switched by the internal clock.
Therefore, the audio signal shared of 5 bands is output
from a serial output terminal.
The 10 bands version using the double by the cascade
connection is prepared.
BPF for the audio spectrum analyzer display of the 5 bands
10 bands extension is available by the cascade connection
BPF using the switched capacitor filter technology
CR oscillation circuit on chip
(External clock input is available)
Power-on initialization circuit on chip
(External reset input is available)
fOSC fOSC/16 fOSC/4 iH
External Resistor connecting terminal.
External Resistor connecting terminal or External clock input terminal.
Both as Reset input terminal
and the clock of (2/3)*fOSC output terminal.
Trigger signal for reading-out the AOUT of each band output terminal.
Peak voltage of each band output terminal.
Audio signal input terminal.
Positive power supply +5.0 V
The peak frequency in each band of NJU7505A are a suitable band interval which is the 5 bands at using
the single and is the 10 bands at using the double by the cascade connection.
Peak Frequency ( Hz )
Using the single
Using the double
Note 1) It may not be output along the expectation at the peak frequency of * marking, since the sampling
time is not enough.
Note 2) The bands of f1a, f2a, ... f5a correspond to the master side and the bands of f1b, f2b, ... f5b
correspond to the slave side at the cascade connection of the double.
The example of using the single
The example of using the double
2/3 x fOSC
• Interface to external controller
The example of the interface between the NJU7505A and the external controller is shown below;
(1) Example of the interface to the external controller ( Using the single )
After the RSTb signal from the external controller is input and then the internal circuit is initialized, each
band data is output as shown below timing chart;
Since the RD signal is output before each band is switched, the external controller is to count the number of
the RD signal and is to recognize the status of the band and is to read the output data from the AOUT terminal
through the external A/D converter.
The output type of the external controller connected to the RSTb/CLKO terminal as the RSTb input should
be the N-channel and open-drain type or the diode should be connected between the RSTb/CLKO terminal
and the output terminal of the external controller, so that the voltage of the RSTb/CLKO terminal is not gotten
over the VSS level.
3 x 214 / fosc
f3 f5 f1
f3 f5 f1
f2 f4 f3 f1
f2 f4 f3
Since the RD signal is output before 248/fOSC
of each band switched, the output data should
be read out within the limited time as shown
248 / fOSC
8 / fOSC
If the RSTb signal which pulse width is
more than 4/fOSC is input, the internal circuit is
initialized and the data of f1 band is output from
the AOUT terminal after 52/fOSC of the rise edge
of the RSTb signal.
4 / fOSC[MIN]
52 / fOSC