U2514B
AM/FM Receiver for Digital Tuning with FM-Stereo Decoder
Description
The U2514B is an integrated bipolar radio suitable for
digital tuning systems. It contains a FM front end with
pre-amplifier and FM-stereo decoder as well as a
complete AM receiver and demodulator. Stop-signal
generation is implemented for FM and AM mode. This
circuit is designed for use in small radios, power packs
and multimedia applications
Features
D
FM wideband AGC
D
LO-buffer for digital tuning
D
Integrated stop signal generation with true
AM/ FM discriminators
D
High cut
D
Mute function
D
Pilot canceller
D
Supply voltage range 3 to 12 V
D
Package: SSO28
D
Adjustable stop signal sensitivity
D
Automatic stereo-mono-blend
Block Diagram
FMOSCE
FMOSCB
FMRF
6
28
FMIN
2
FMAGC
8
OSCOUT
GNDRF
4
AM FM stop
signal detect
20
Pilot PLL
23
CTRLB
27
1
AMIN
AM front end
AM IF +
demodulator
Control
unit
VS
V
Ref
GND
16
7
AMOSC
IFOUT
10
12
FMIFIN
AMIFIN
13
17
METER
9
22
26
AMFM
14
VREF
12305
AFSM
FMDET
15
11
MPXOUT
25
MPXIN
24
Matrix
decoder
+ HCC
18
OUTR
19
OUTL
21
LPF
5
3
FM front end
FM IF +
demodulator
CERES
CTRLA
AMSADJ
Figure 1.
TELEFUNKEN Semiconductors
Rev. A2, 04-Nov-96
1 (15)
Preliminary Information
U2514B
Pin Description
Pin
1
2
3
4
5
6
7
8
9
FMOSCB 6
AMOSC 7
OSCOUT 8
AMSADJ 9
IFOUT 10
AFSM
11
23 CTRLB
22 CTRLA
21
LPF
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Function
AM antenna input
FM-AGC time constant
FM RF tank
Ground RF
FM oscillator emitter
FM oscillator basis
AM oscillator
Buffered AM/FM oscillator
output
AMSADJ Current-input for AM stop signal
adjust
IFOUT AM/FM IF output
AFSM
AF smoothing voltage
FMIFIN FM IF amplifier input
AMIFIN AM IF amplifier input
VREF
Reference voltage
FMDET FM discriminator output
GND
Ground
METER Fieldstrength voltage output
OUTR
AF output right
OUTL
AF output left
CERES Resonator 456 kHz
LPF
Low pass filter for Pilot-PLL
CTRLA Control input for mute, search
mode and search sensitivity
CTRLB Control input for forced mono,
control output for stop function
and stereo information
MPXIN Stereo decoder MPX input
MPXOUT AM/FM MPX output
AMFM AM/FM switch and pilot
canceller time constant
VS
Supply voltage
FMIN
FM antenna input
Symbol
AMIN
FMAGC
FMRF
GNDRF
FMOSCE
FMOSCB
AMOSC
OSCOUT
AMIN 1
FMAGC 2
FMRF
GNDRF
FMOSCE
3
4
5
28 FMIN
27 VS
26 AMFM
25 MPXOUT
24 MPXIN
20 CERES
19
18
17
16
15
10547
OUTL
OUTR
METER
GND
FMDET
FMIFIN 12
AMIFIN 13
VREF 14
24
25
26
27
28
Figure 2. Pinning
Ordering and Package Information
Extended Type Number
U2514B-AFN
U2514B-AFNG3
Package
SSO28
SSO28
Remarks
Taping according to ICE-286-3
2 (15)
Preliminary Information
TELEFUNKEN Semiconductors
Rev. A2, 04-Nov-96
U2514B
Pin Description
FMIN, FMAGC, FMRF
FMOSCE, FMOSCB
FMOSCB
3
VREF
FMRF
MIXER
6
FMOSCE
5
FMAGC
1.2 k
FM
ON
T
1
T
2
2
I
AGC
GNDRF
Figure 4.
12415
FMIN
28
1.5 k
FM
ON
GNDRF
12414
Figure 3.
The FM local oscillator consists of a transistor in
grounded collector configuration. The negative
resistance at the base of the transistor is generated by an
external capacitor connected between emitter FMOSCE
(Pin 5) and GNDRF (Pin 4) An other external capacitor
is connected between base FMOSCB (Pin 6) and emitter
FMOSCE (Pin 5) which increases the resistance at the
emitter and leads to a higher oscillator swing. The
negative resistance at FMOSCB is approximately 250
W
.
Therefore, the resonant LO tank resistance of
approximately 5 k
W
(depends on Q-factor of the coil) is
transformed to this magnitude via a capacitor.
OSCOUT
8
The FM pre-amplifier input FMIN (Pin 28) consists of a
transistor grounded base circuit (T
2
) which provides
excellent noise performance and large signal behavior. It
is recommended to connect a source impedance of 100
W
in order to achieve optimal performance. The dc current
through the amplifying transitor is reduced by the internal
AGC. This means in the case of large input signals, the
input ac current is bypassed via the wideband AGC
transistor T
1
. A capacitor is connected between FMAGC
(Pin 2) and GNDRF (Pin 4). It shortens the transistor base
to GNDRF and it also serves for smoothing of the AGC
voltage. A tuned RF circuit is connected between FMRF
(Pin 3) and VS (Pin 27). The amplified RF signal is fed
internally to the mixer input.
OSCOUT
FM
AM
12416
Figure 5.
A resistor is connected between OSCOUT (Pin 8) and
VREF (Pin 14). It determines the amplitude of oscillator
voltage which is fed to the PLL circuit. The TEMIC PLL
familiy U428xBM is recommended because it offers high
signal to noise ratio and low current consumption.
TELEFUNKEN Semiconductors
Rev. A2, 04-Nov-96
3 (15)
Preliminary Information
U2514B
AMIN
VREF
AMSADJ
12418
9
AMSADJ
AMIN
1
GND
I
AGC
GNDRF
Figure 6.
Figure 8.
12417
The AM antenna coil is connected between AMIN (Pin 1)
and VREF (Pin 14). In order to ensure that the AGC
operates correctly, a coil impedance of approximately 25
k
W
is necessary.
AMOSC
7
AMOSC
The ceramic resonator of the stereo decoder PLL circuit
is used as a stop signal detector for AM signals. For this
purpose, the parallel resonance frequency of the
resonator, which is unloaded about 456 kHz, is reduced
by an internal load capacitor down to 455 kHz. Therefore,
the AM IF must be 455 kHz. The internal loading
capacitor is defined by the current through AMSADJ
(Pin 9) to GND. An external resistor is connected
between AMSADJ (Pin 9) and GND. It allows the
alignment of the stop signal center frequency. The width
of the stop window is typicaly 800 Hz. If AM search-
mode is not activated, the pin is internally pulled to
ground.
VREF
IFOUT
6k
AM
ON
FM
12419
10
IFOUT
AM
GNDRF
Figure 7.
Figure 9.
12420
The AM oscillator has to be loaded by an external tank
referred to VREF (Pin 14). If reduction of the oscillator
voltage is necessary, this may be achieved by a parallel
resistor.
The IF output (IFOUT Pin 10) of both the FM and the AM
mixer has to be loaded into external IF-tank circuits
refered to VREF (Pin 14). Q-factor of IF coils must not be
lower than 50.
4 (15)
Preliminary Information
TELEFUNKEN Semiconductors
Rev. A2, 04-Nov-96
U2514B
AMIFIN
FMDET
VREF
VREF
3.3 k
13
AMIFIN
12421
15
FMDET
150
m
A
12422
Figure 10.
Figure 12.
The input impedance of the AM IF amplifier is 3.3 k
W
according to the required impedance of most ceramic
filters. The input refers to VREF (Pin 14).
The discriminator allows the connection of a ceramic
resonator or LC tank. A minimization of THD and
adjustment of center frequency versus temperature can
only be achieved by using a LC tank. This performs a
temperature independent stop signal.
FMIFIN
AFSM
25
40
m
A
100 k
12
MPXOUT
11
AFSM
FMIFIN
12423
GND
Figure 13.
Figure 11.
12424
The input impedance of the FM IF amplifier is 330
W
according to the required impedance of most FM ceramic
filters. The input referes to GND (Pin 16).
A capacitor is connected between AFSM (Pin 11) and
GND for smoothing of the FM-AF. This is necessary to
generate a modulation independent stop signal. (Because
the deviation of the FM signal (75 kHz) can be greater
than the stop signal window (25 kHz)). In the
AM-search-mode, the external capacitor smoothes the
demodulated AM-IF-signal.
TELEFUNKEN Semiconductors
Rev. A2, 04-Nov-96
5 (15)
Preliminary Information
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