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Audio ICs
Band-pass filter for spectrum analyzer
BA3826S
The BA3826S is a 7-band ( 2), band-pass filter that uses microprocessor time division to output in serial to left and right stereo channels. To minimize the number of external components required and enable compact and reliable designs, all of the capacitors for the filters are on the chip. FApplications CD radio cassette players, mini-component stereo systems, car stereos FFeatures 1) Seven band-pass filter elements for spectrum analyzer displays. 2) Microprocessor time division used for serial output on L and R channels. 3) All filter capacitors are built-in to minimize external attached requirements. FAbsolute maximum ratings (Ta = 25_C)
4) Low current dissipation (8mA Typ.). 5) Ideal for mini-component stereos and other stereo equipment.
FRecommended operating conditions (Ta = 25_C)
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Audio ICs
FBlock diagram
BA3826S
FElectrical characteristics (unless otherwise noted, Ta = 25_C, VCC = 5V, Vee = *5V, RL = 10k, and R = 120k)
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Audio ICs
FMeasurement circuit
BA3826S
FCircuit operation (1) Input switch circuit The BA3826S alternately switches between the left and right stereo channel signals using time division to serialize and process the signals.
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Audio ICs
(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). (4) Timing
BA3826S
(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.
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 restrictions 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 characteristic.
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(b) For DET, after release of RESET, there is a discharge time of 14mS (Max.) The read enable period for Vo starts 0.5ms after the output switch logic settles.
BA3826S
(6) Output switch circuit This circuit uses time division switching to output the peak hold signal from each DET. Switching occurs when the control signal reaches 1.4V, and when A, B, and C are all high, output is disabled (GND level). Refer to the table below regarding the output switching logic. The recommended output load resistance is 10k.
(5) Application example with reduced cycle time The transition characteristics for the band-pass filter are shown in the graph below. The time for at least 5 fo cycles is required until the DET output peaks. Therefore, the lower the frequency, the longer the time required and fo1 requires the longest time. Refer to the values given below for applications that require a shorter cycle time. When fo1 = 60Hz, the time requires for output u 60% is tg u 45ms.
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Audio ICs
FInput / output switching logic Input switching logic Output switching logic
BA3826S
FApplication example
FOperation notes (1) Application circuits Provided the recommended circuit constants are used, the application circuits 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.
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(2) Frequency characteristics The frequency characteristics for this IC are set by an external resistor. The value of this resistor for the specification conditions is 120k. Use a potentiometer if you wish to set the frequency characteristics accurately. (3) Operating voltage range Operation of the application example circuit is guaranteed provided that the VCC and Vee voltages are within the specified power supply voltage range, and the ambient temperature is within the specified range. With regard to the characteristic values, the output voltage level will differ from the rated values for the specification conditions if the power supply voltage is reduced, but the inherent function of the band-pass filters is preserved.
BA3826S
(4) Load resistance The various circuit characteristics in this specification sheet were measured using an output load resistance of 10k. If the load resistance is too low, the I / O gain and control range vary slightly. Be aware of this when connecting the next stage. (5) Coupling capacitors Set the polarity of the input electrolytic coupling capacitors after establishing the electrical potential relationship with the connected input.
FElectrical characteristics curves
FExternal dimensions (Units: mm)
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