U4254BM-M Datasheet, PDF (5/14 Pages) ATMEL Corporation – Low-noise AM/FM Antenna Impedance Matching IC

AMIN
AMOUT, AMOUT1
U4254BM-M
The AM input has an internal bias voltage. The DC voltage at this pin is V_Ref1/2. The input
resistance is about 470 kΩ. The input capacitance is less than 10 pF.
Figure 8. Internal Circuit at Pin AMIN
VREF1/2
8
AMIN
470 kΩ
ESD
The buffered AM amplifier consists of a complementary pair of CMOS source followers.
The transistor gates are connected to AMIN. The pin AMOUT is the NMOS transistor's
source, pin AMOUT1 is the PMOS transistor's source. Due to the two different DC levels
of these pins, they have to be connected together via an external capacitor of about
100 nF. By means of this technique an excellent dynamic range can be achieved.
Figure 9. Internal Circuit at Pins AMOUT1 and AMOUT
AMOUT1
11
ESD
AMOUT
10
ESD
VREF1
VREF1 is the stabilized voltage for the AM amplifier and the AGC block. To achieve
excellent noise performance at LW frequencies, it is recommended that this pin be con-
nected to ground via an external capacitor of about 1 µF.
5
4772B–AUDR–11/03