TDA7427A Datasheet, PDF (6/21 Pages) STMicroelectronics – AM-FM RADIO FREQUENCY SYNTHESIZER AND IF COUNTER

TDA7427A
GENERAL DESCRIPTION
This circuit contains a frequency synthesiser and
a loop filter for use in FM/AM radio tuning sys-
tems. Only a VCO is required to build a complete
PLL system. For auto search/stop operation an IF
counter system is available.
For FM and SW AM application, the counter
works in a two-stage configuration. The first stage
is a swallow counter with a two modulus (:32/33)
precounter. The second stage is an 11-bit pro-
grammable counter.
For LW and MW application, a 16-bit programma-
ble counter is available.
The circuit receives the scaling factors for the pro-
grammable counters and the values of the refer-
ence frequencies via a I²C bus interface.
The reference frequency is generated by an inter-
nal XTAL oscillator followed by the reference di-
vider. The device can operate with XTAL oscilla-
tor between 4 and 13MHz either in master mode
and in slave mode.
The reference and step frequencies are free se-
lectable. (XTAL frequency divided by an integer
value). The outputs signals of the phase detector
are switching the programmable current sources.
The loop filter integrates their currents to a DC
voltage.
Values of the current sources are programmable
by 6 bits also received via the I²C bus.
To minimize the noise induced by the digital part
of the system, a separate power supply supplies
the internal loop filter amplifier. The loop gain can
be set for different conditions by setting the cur-
rent values of the charge/pump generator.
IF COUNTER SYSTEM
Two separate inputs are available for AM and FM
IF signals. The level of integration is adjustable
by six different measuring cycle times.
The tolerance of the accepted count value is ad-
justable, to reach an optimum compromise for
search speed and precision of the evaluation.
For the FM range the center frequency of the
measured count value is adjustable in 32 steps,
to get the possibility of fitting the IF filter toler-
ance. In the AM range an IF frequency of 448 to
479KHz ( 10.684 to 10.715MHz for AM up-con-
version) with 1KHz steps is available.
PLL FREQUENCY SYNTHESIZER
Input Amplifiers
The signals applied on AM and FM inputs are am-
plified to get a logic level in order to drive the fre-
quency dividers.
The typical input impedance for FM and AM in-
puts is 4kΩ.
Table 1. Address Organization
FUNCTION
PLL CHARGE PUMP
PLL COUNTER
PLL COUNTER
PLL REF COUNTER
PLL REF COUNTER
PLL LOCK DETECT
IFC REF COUNTER
IFC REF COUNTER
IFC CONTROL
IFC CONTROL
OSC ADJUST
PORT EXTENSION
SUBAD
00H
01H
02H
03H
04H
05H
06H
07H
08H
09H
0AH
0BH
BIT 7
LPIN1/2
PC7
PC15
RC7
RC15
LDENA
IRC7
IFCM1
IFENA
IFS2
-
-
MSB
BIT 6 BIT 5
CURRH B1
PC6
PC5
PC14 PC13
RC6
RC5
RC14 RC13
INLOCK D3
IRC6 IRC5
IFCM0 IRC13
-
-
IFS1
IFS0
-
-
-
DOUT3
BIT 4
B0
PC4
PC12
RC4
RC12
D2
IRC4
IRC12
-
CF4
OSC4
DOUT4
BIT 3
A3
PC3
PC11
RC3
RC11
D1
IRC3
IRC11
-
CF3
OSC3
DOUT5
BIT 2
A2
PC2
PC10
RC2
RC10
D0
IRC2
IRC10
EW2
CF2
OSC2
DOUT6
BIT 1
A1
PC1
PC9
RC1
RC9
PM1
IRC1
IRC9
EW1
CF1
OSC1
DOUT2
LSB
BIT 0
A0
PC0
PC8
RC0
RC8
PM0
IRC0
IRC8
EW0
CF0
OSC0
DOUT1
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