4

4528M–AUDR–03/08

T4260

3.

Functional Description

The T4260 implements an AM up-conversion reception path from the RF input signal to the IF

output signal. A VCO and an LO prescaler for AM are integrated to generate the LO frequency to

the AM mixer. The FM reception path generates the same LO frequency from the RF input sig-

nal by a down-conversion to the IF output. The IF A/D output is designed for digital signal

processing. The IF can be chosen in the range of 10 MHz to 25 MHz. Automatic gain control

(AGC) circuits are implemented to control the preamplifier stages in the AM and FM reception

paths.

For improved performance, the PLL has an integrated special 2-bit shift fractional logic with spu-

rious suppression that enables fast frequency changes in AM and FM mode by a low step

frequency (f

alignment via a microcontroller.

For a double-tuner concept, external voltage can be applied at the input of the DACs, the inter-

nal PLL can switched off and the OSC buffer (output) can also be used as input.

Several register bits (bit 0 to bit 145) are used to control the circuit’s operation and to adapt cer-

tain circuit parameters to the specific application. The control bits are organized in four 8-bit, four

16-bit and three 24-bit registers that can be programmed by the 3-wire bus protocol. The bus

protocol and the bit-to-register mapping is described in Section 8. “3-wire Bus Description” on

page 10. The meaning of the control bits is mentioned in the following sections.

21

OSCB

Oscillator base

22

OSCBUF

Oscillator buffer output/input

23

EN

3-wire bus Enable

24

CLK

3-wire bus Clock

25

DATA

3-wire bus Data

26

VRPLL

PLL reference voltage

27

REFFREQ

PLL reference frequency

28

GNDPLL

PLL ground

29

IFOUTB

IF output B

30

IFOUTA

IF output A

31

IFAGCFM

FM IF-AGC filter

32

IFAGCA1

AM IF-AGC filter 1

33

RFAGCFM

RF FM-AGC filter

34

IFREF

IF amplifier reference input

35

IFINAM

IF amplifier AM input

36

IFINFM

IF amplifier FM input

37

VRT

Tuner reference voltage

38

GNDT

Tuner ground

39

MXAMOB

AM mixer output B

40

MXAMOA

AM mixer output A

41

VST

Tuner supply voltage

42

RFAGCA1

RF AM-AGC filter 1

43

MXFMOA

FM mixer output A

44

MXFMOB

FM mixer output B

Table 2-1.

Pin Description (Continued)

Pin

Symbol

Function