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Audio ICs
FM / TV front end
BA4424N
The BA4424N is a monolithic IC designed for FM front end use. It consists of an RF amplifier circuit, mixer circuit, local oscillation circuit, IF buffer amplifier, and a variable capacitor-diode for AFC.
FFeatures 1) An RF amplifier, mixer, local oscillator, IF buffer amplifier, and AFC diode are included on-chip. 2) Reception of VHF terrestrial TV channels is possible. 3) Uses a double balance mixer to improve intermodulation characteristics. 4) Includes a clamp diode in the mixer output. 5) Local oscillation buffer on-chip for improved response to strong input. 6) The output impedance of the IF buffer amplifier is matched with the ceramic filter impedance at 330. FAbsolute maximum ratings (Ta = 25_C)
7) A resistive load can also be used for the mixer output. 8) Mixer input coupling capacitor included on-chip. 9) Includes a feedback capacitor for the local oscillation circuit. 10) Compact 9-pin SIP package. Pins arranged for convenient mounting.
FRecommended operating conditions (Ta = 25_C)
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Audio ICs
FBlock diagram
BA4424N
FElectrical characteristics DC characteristics (unless otherwise noted, Ta = 25_C, VCC = 4V, no input)
AC characteristics (unless otherwise noted, Ta = 25_C and VCC = 4V)
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Audio ICs
FMeasurement circuit
BA4424N
FPin connections 1 FM ANT input pin
2 3 4 5
: Connect to BPF ZIN = 75 RF amplifier bypass pin : Connect to bypass capacitor RF amplifier output load pin : Connect to RF tuning circuit MIX output pin : IFT or resistor load GND pin : IC ground pin
6 IF amplifier output pin 7 AFC diode pin
8 OSC pin 9 VCC pin
: ZOUT = 330 : Cathode pin (anode pin is connected internally to ground) : Connect to resonating circuit : IC voltage supply pin
FCircuit operation (1) RF amplifier circuit The RF amplifier consists of a common base transistor. A band pass filter (BPF) is used in the ANT circuit, and as the RF amplifier is base-grounded, a BPF with an output impedance of 75 should be used. If a BPF without DC cutoff is used, a coupling capacitor will be necessary. An LC tuning circuit is connected to form the output load of the RF amplifier. A coil with tap or coil with secondary winding can be used to reduce spurious ratios such as image ratios. A coupling capacitor for the mixer circuit is included on-chip. The bypass capacitor for the RF amplifier should have good high frequency characteristics, and it should be connected to the input BPF ground connection as close as possible to Pin 5 (GND), such that the connection pattern absolutely does not allow supply current to flow from Pin 5.
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Audio ICs
(2) Mixer circuit The mixer circuit is a double balance type with minimal OSC leakage and little spurious interference. The mixer output includes a diode limiter for improved response to strong input signals.
BA4424N
(4) IF buffer amplifier circuit The IF buffer amplifier consists of an emitter-follower amplifier circuit. The output impedance is set in the IC to 330, and it can be directly connected to a ceramic filter.
In addition to an IFT, a resistive load can also be used for the mixer output load. However, take care in this case as the gain will fall. (3) Local oscillation circuit The local oscillation circuit is a Colpitts circuit with grounded collector. The capacitor between the base and emitter and the capacitor between the collector and emitter which form the oscillation circuit are included on the IC. A buffer has been added for input to the mixer circuit to protect the circuit when strong input is present. R8 is to prevent spurious radiation. Take care when setting the value.
(5) Variable capacitor-diode for AFC A variable capacitor-diode is included in the IC for AFC. Utilize the FM detection output as AFC signal. The anode is connected to ground.
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Audio ICs
FOperation notes (1) Application circuit The example application circuit is the one which we recommend, however, when using it, verify characteristics carefully. If external circuit values are changed, set them with sufficient margin to allow for deviations of both the Rohm IC and external components in the quiescent and transient characteristics. Also, please note that we have not completely verified any possible patent issues which the application circuit may involve. (2) Operating power supply voltage range As long as the operating power supply voltage range is not exceeded, the circuit functions are guaranteed within the ambient operating temperature. Although we cannot guarantee that the electrical characteristic values rated under the rating conditions will be obtained, there will be no abrupt changes in the characteristics within this range. (3) RF amplifier A band pass filter (BPF) is used in the ANT circuit, and as the RF amplifier is base-grounded, a BPF with an output impedance of 75 must be used. If a BPF without DC cutoff is used, a coupling capacitor will be necessary. Connect the bypass capacitor to the ground connection of the input BPF. The pattern connecting these should be such that supply current will absolutely not flow from Pin 5 (the ground line should be laid in the same fashion as shown in the measurement circuit schematic).
BA4424N
(4) Mixer load In addition to an IFT, a resistive load can also be used for the mixer output load. However, take care in this case as the gain and intermodulation characteristics will be affected. (5) Local oscillation circuit To reduce spurious radiation, the oscillation level at Pin 8 (OSC) can be adjusted. This is done by adding a resistor (several to several tens of ) between Pin 8 and the tank circuit. However, when setting the value, take care regarding the oscillation margin as related to the tank circuit Q damp. (6) IF buffer amplifier If the buffer amplifier pin is connected to another circuit to use the buffer amplifier pin's voltage, take care that a reverse voltage never appears at the pin. (7) Power supply RC filter Do not insert a resistor between the VCC pin (Pin 9) and the MIX OUT pins (Pins 3 and 4), as a resistor inserted in the power supply line will decrease sensitivity due to the drop in the voltage. Regarding the resistor between Pin 9 and the RFout pin (Pin 3), set the value so that the voltage at Pin 3 is not lower than the voltage at Pin 2.
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Audio ICs
FElectrical characteristic curves
BA4424N
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Audio ICs
BA4424N
FExternal dimensions (Units: mm)
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