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IF Signal Processing for DAB
U2759B
Description
The U2759B is a bipolar integrated IF signal processing circuit. It is designed for DAB (Digital Audio Broadcasting)
applications.
Features
D High linearity of the complete circuit
D 3-stage gain controlled wideband amplifier
D Internal AGC loops
D AGC time constants and thresholds adjustable
D Mixer: double balanced high current Gilbert Cell
Block Diagram
IF1IN
IF1IN
16
1
AGCPRE 3
THRPRE 2
DC
11
9144
89
LO LO
5
AGCT
Figure 1.
10
THRIF
6 IF2OUT
7
NC
Bandgap 14 VS
12 13
VREF BG
4
GND
15
GND
Ordering and Package Information
Extended Type Number
U2759B-A
U2759B-AFL
U2759B-AFLG3
Package
DIP16
SO24
SO24
Remarks
Taping according ICE-286-3
TELEFUNKEN Semiconductors
Rev. A1, 06-Sep-96
Preliminary Information
1 (9)

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U2759B
Pin Description
IF1IN 1
16 IF1IN
THRPRE 2
15 GND
AGCPRE 3
14 VS
GND 4
13 BG
AGCT 5
12 VREF
IF2OUT 6
NC 7
11 DC
10 THRIF
LO 8
12585
9 LO
Figure 2. Pinning DIP16
IF1IN 1
THRPRE 2
24 IF1IN
23 GND
NC 3
22 NC
AGCPRE 4
21 NC
GND 5
20 VS
AGCT 6
19 BG
NC 7
18 VREF
IF2OUT 8
17 DC
NC 9
16 THRIF
NC 10
15 NC
NC 11
14 NC
LO 12
13 LO
12584
Figure 3. Pinning SO24
Pin Symbol
Function
1 IF1IN IF1 input
2 THRPRE AGC-threshold for pre-amplifier
3 AGCPRE AGC for pre-amplifier
4 GND Ground
5 AGCT AGC time constant for
IF amplifier
6 IF2OUT IF2 output
7 NC Not connected
8 LO Local oscillator
9 LO Local oscillator
10 THRIF AGC-threshold for IF amplifier
11 DC DC-level
12 VREF Reference voltage
13 BG Bandgap
14 VS Supply voltage
15 GND Ground
16 IF1IN IF1 input
Pin Symbol
Function
1 IF1IN IF1 input
2 THRPRE AGC-threshold for pre-amplifier
3 NC Not connected
4 AGCPRE AGC for pre-amplifier
5 GND Ground
6 AGCT AGC time constant for
IF amplifier
7 NC Not connected
8 IF2OUT IF2 output
9 NC Not connected
10 NC Not connected
11 NC Not connected
12 LO Local oscillator
13 LO Local oscillator
14 NC Not connected
15 NC Not connected
16 THRIF AGC threshold for IF amplifier
17 DC DC-level
18 VREF Reference voltage
19 BG Bandgap
20 VS Supply voltage
21 NC Not connected
22 NC Not connected
23 GND Ground
24 IF1IN IF1 input
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Preliminary Information
Rev. A1, 06-Sep-96

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U2759B
Pin Description for DIP16
IF1IN
The input voltage is fed via Pins 1 and 16 to the first stage
of the 3 stage gain-controlled wide-band amplifier. The
first stage has an internal dc voltage supply with an
internal resistance of 2 kW to connect the SAW filters
directly.
AGCPRE
Pin 3 is an open-collector output. Depending on the input
level, a control voltage can be generated for the external
pre-stage by using an external voltage divider. This
prevents an overdrive of input IF1. The threshold for
activation of the open-collector output is adjusted with
Pin 2.
1 1.2 kW
1.2 kW
9229
16
3
3 kW 3 kW
9227
Figure 4.
THRPRE
The control of a pre-stage can be adjusted at Pin 2 by using
an external potentiometer switched against ground. With
increasing voltage at Pin 2, control of the (external) pre-
stage does not become active until there is a high input
level at IF1. If Pin 2 is not connected, the control only
becomes active if the input is overdriven.
Figure 6.
IF2OUT
The product of input signal IF1 and the oscillator
frequency (Pins 8 and 9) can be found at Pin 6. Here it
concerns the emitter follower output with integrated
current sink. The output voltage IF2 is twice as high as the
difference between the voltage at Pin 10 and Pin 11.
6
3 kW
2 kW
Figure 5.
2
9228
9242
Figure 7.
TELEFUNKEN Semiconductors
Rev. A1, 06-Sep-96
Preliminary Information
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U2759B
LO
The externally generated oscillator frequency is supplied
via crosspoint capacitances at Pin 8 and /or Pin 9. If the
oscillator frequency is not symmetrically connected, each
open pin has to be blocked against ground.
AGCT
The control voltage for the wide–band amplifier is
generated by using the external capacitor at Pin 5. By
integration of the control current generated in the IC,
there is a high control voltage if there is a large input level
at IF1 and a low control voltage if there is a low input
level.
8
9
5.6 kW
5.6 kW
50 W
9243
9230
5
Figure 10.
Figure 8.
DC
The dc mean value of the output signal is adjusted by
using an external voltage at Pin 11. The voltage at Pin 11
always has to be higher than the voltage at Pin 10.
THRIF
The control threshold for the AGC is adjusted by using an
external voltage.
5 kW
11
9245
Figure 9.
10
Figure 11.
9244
4 (9) TELEFUNKEN Semiconductors
Preliminary Information
Rev. A1, 06-Sep-96

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U2759B
VREF
Functional Description
A stabilized voltage is available at Pin 12 on to which an
external voltage divider for supplying Pin 10 and Pin 11
can be connected.
At Pin 13, the internally generated temperature stable
reference voltage is blocked against ground. This voltage
must not be loaded by external circuitry.
More information concerning the parameters:
Noise ratio of all ICs:
Typically 11.2 dB (SSB)
Intercept point 3rd order:
Typically 58 dB (2 Vss at Pin 6)
13
12
The U2759B consists of a controllable wideband ampli-
fier, a mixer and AGC-block.
The input voltage Vif1 is applied at Pin 1 and 16 and it is
fed via a 3-stage controlled wideband amplifier to the
mixer. The oscillator voltage can be applied symmetri-
cally as well as unsymmetrically.
The mixed signal is used in order to generate the AGC-
voltage. The mixed signal therefore is fed to a comparator
which charges or discharges an external capacitor depen-
dent on the signal level. The threshold of the comparator
can be adjusted externally. The generated voltage con-
trols the wideband amplifier.
The generated control voltage can be used also for an
additional external preamplifier. This AGC protects the
IF1 input against overload.
The amplitude as well as the superimposed DC-level of
the output voltage VIF2 can be adjusted by an external
voltage. VREF is therefore available at Pin 12 (max.
500 m A).
Upper limiting threshold
4.5 V
9246
Figure 12.
DC-level
(Pin 11)
VP (Pin 6)
IF AGC threshold
(Pin 10)
1.7 V
Lower limiting threshold
12586
Figure 13. Adjustment of output level
TELEFUNKEN Semiconductors
Rev. A1, 06-Sep-96
Preliminary Information
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