ROHM BA4424N Datasheet

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.

Features

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 330Ω.

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.

Absolute maximum ratings (Ta = 25C)

Recommended operating conditions (Ta = 25C)

48

Audio ICs BA4424N

Block diagram

Electrical characteristics

DC characteristics (unless otherwise noted, Ta = 25C, V

CC = 4V, no input)

AC characteristics (unless otherwise noted, Ta = 25C and V

CC = 4V)

49

Audio ICs BA4424N

Measurement circuit

Pin connections

FM ANT input pin : Connect to BPF ZIN =

1

75Ω

RF amplifier bypass pin : Connect to bypass ca-

2

pacitor

RF amplifier output load pin : Connect to RF tuning

3

circuit

MIX output pin : IFT or resistor load

4

GND pin : IC ground pin

5

IF amplifier output pin : ZOUT = 330Ω

6

AFC diode pin : Cathode pin (anode pin

7

is connected internally
to ground)

OSC pin : Connect to resonating

8

circuit

VCC pin : IC voltage supply pin

9

Circuit 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 75Ω 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.

50