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Audio ICs
Band-pass filter for spectrum analyzer
BA3834S / BA3834F
The BA3834S and BA3834F are 7-band, band-pass filter ICs that use microprocessor time division to produce serial
output for spectrum analyzer displays. To minimize the number of attached components required and enable compact
and reliable designs, all of the capacitors for the filters are on the chip.
Applications
CD radio cassette players, mini-component stereo systems, car stereos
Features
1) Seven band-pass filter elements for spectrum analyzer displays.
2) High-speed readout
(output response time: 5µsec. Typ.).
Absolute maximum ratings (Ta = 25C)
3) Discharge time constant circuit for each band is on
the chip.
4) Differential input amplifier rejects common-mode
noise.
5) Single 5V power supply.
Recommended operating conditions (Ta = 25C)
591
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Audio ICs BA3834S / BA3834F
Block diagram 1 (BA3834S)
592
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Audio ICs BA3834S / BA3834F
Block diagram 2 (BA3834F)
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Audio ICs BA3834S / BA3834F
Electrical characteristics (unless otherwise noted, Ta = 25C, VCC = 5V, RL = 10MΩ, VAIN = 30dBV and
SEL = 1)
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Audio ICs BA3834S / BA3834F
Measurement circuit (BA3834S)
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Audio ICs BA3834S / BA3834F
Output select logic table
Timing chart
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Audio ICs BA3834S / BA3834F
Application example (BA3834S)
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Audio ICs BA3834S / BA3834F
Operation notes
(1) Frequency characteristics
The frequency characteristics of this IC are determined
by the resistor connected between the R
REF terminal and
GND. For the specification conditions, the value of this
resistor is 100kΩ. If it is necessary to set the frequency
characteristics accurately, use a variable resistor (note:
all bands will shift together).
(2) Load characteristics
T o convert the bias sense output signal to the GND sense
signal, the IC performs a V/I conversion, and then an I/V
conversion using a 10kΩ resistor (Typ.) for the output.
Therefore, if the load circuit connected to the AOUT pin
has a MOS structure there is no problem (eg. microprocessor input port), but if the connected circuit has a low
input impedance, it may cause the output level to drop.
(3) External resistor for the control pin
When using a common port for the output select control
and FL drive, you must add a diode and resistor as shown
in Fig. 4 to prevent the FL drive “L” voltage from destroying the IC.
And from this, the following condition is obtained:
R t 30kΩ
In this case, the “L” level voltage V
V
2 t 0.75V
2 for the IC will be:
(4) Recommended operating ranges
Provided that the IC is operated within the recommended
operating conditions and the recommended temperature
range, the basic circuit functions are guaranteed. Within
these ranges, ratings for electrical characteristics for
conditions other than those stipulated cannot be guaranteed, but the inherent function of the bandpass filter will
be maintained.
(5) Application example
Provided the recommended circuit constants are used,
the application example should function correctly. However, we recommend that you confirm the characteristics
of the circuits in actual use and pay due attention to the
cautionary notes given below.
If you change the circuit constants, check both the static
and transient characteristics of the circuit, and allow sufficient margin to accommodate variations between both
ICs and external components. Note, also, that Rohm has
not been able to conduct a sufficient study into patent
rights.
In this case, the “L” voltage applied to the internal
comparator input terminal V
R1)R
1 = VREF
V
1)R2)R
R
1 is given by:
T o maintain a noise margin of at least 2.5V with respect to the comparator threshold level V
representative values for V
REF, R1 and R2 are 1.5V,
20kΩ, and 10kΩ respectively. This gives:
20kΩ)R
20kΩ)10kΩ)R
1.5V)0.25Vt1.5V
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REF, the
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Audio ICs BA3834S / BA3834F
(6) Output offset voltage
The relationship between the output offset voltage and
the output selection cycle (cycle time) for this IC is shown
in Fig.5. The maximum output offset voltage of 150mV
that is given in the electrical characteristics table is under
the condition that T s = 200msec. When T s is greater than
50msec, the graph of the output offset voltage is a
straight line at 150mV . When T s is below 50msec, due to
transient characteristics of the peak hold circuit, the
graph is a line sloping downwards to the right. In other
words, the shorter the cycle, the larger the output offset
voltage.
Furthermore, the output offset voltage may shift due to
soldering or other temperature stresses from the surroundings. Therefore, when setting the spectral analyzer
light level, take into consideration the points given above
and make sure that it does not light by mistake during
quiescent periods. Use the chart below as a guide for
this, and, if necessary, leave even a larger margin.
Electrical characteristics curves
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Audio ICs BA3834S / BA3834F
External dimensions (Units: mm)
600
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