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U4065B Schematic ( PDF Datasheet ) - ATMEL Corporation

Teilenummer U4065B
Beschreibung FM Receiver IC
Hersteller ATMEL Corporation
Logo ATMEL Corporation Logo 




Gesamt 34 Seiten
U4065B Datasheet, Funktion
Features
On-chip Control Functions are Available for System Gain Adjust
(dB Linear versus DC Current)
Low Noise LO Design
ESD Protected
Benefits
All Front-end Functions of a High-performance FM Receiver Except the RF
Preamplifier are Integrated
Improved Dynamic Range by High Current Double-balanced Mixer Design and a New
AGC Conception with 3 Loops On-chip
Improved Blocking and Intermod Behavior Due to a Unique “Interference” Sensor
Controlling the AGC
Easy Cascading of 3 IF Filters (Ceramic) Enabled by Two On-chip IF Preamplifiers
FM Receiver IC
U4065B
Description
The IC U4065B is a bipolar integrated FM front-end circuit. It contains a mixer, an
oscillator, two IF preamplifiers and an unique interference sensor. The device is
designed for high-performance car radio and home receiver applications.
Rev. 4807A–AUDR–05/04






U4065B Datasheet, Funktion
GAINIF1
IF2IN
Figure 6. Gain Control of the First IF Amplifier
17 VREF
2 k
4 ESD
The gain of the first IF amplifier can be adjusted by a resistor to ground. This is useful,
for example, to compensate for the insertion loss tolerances of the ceramic BPFs. It
must be ensured that the output current of the pin does not exceed 150 µA in any case.
Linear increasing in the current out of GAINIF1 results in a linear dB increase of the gain
(0.15 dB/µA).
I4 = 0, thus, G = Gmin = 2 dB
I4 = 140 µA, thus, G = Gmax = 22 dB
Figure 7. Input of the Second IF Amplifier
VREF
5
ESD
The parallel input resistance is 330 . The parallel input capacitance is about 12 pF. No
DC current is allowed. To avoid overload of this stage, an internal detector watches the
input level and causes current at the AGCOUT pin.
6 U4065B
4807A–AUDR–05/04

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U4065B pdf, datenblatt
Functional Description
The U4065B FM-frontend IC is the dedicated solution for high-end car radios. A new
design philosophy enables to build up tuners with superior behavior. This philosophy is
based on the fact that the sensitivity of state of the art designs is at the physical border
and cannot be enhanced any more. On the other hand, the spectral power density in the
FM-band increases. An improvement of reception can only be achieved by increasing
the dynamic range of the receiver. This description is to give the designer an introduc-
tion to get familiar with this new product and its philosophy.
The Signal Path
The U4065B offers the complete signal path of an FM-frontend IC including a highly lin-
ear mixer and two IF preamplifiers. The mixer is a double-balanced, high-current Gilbert
Cell. A high transit frequency of the internal transistors enables the use of the emitter
grounded circuit with its favorable noise behavior. The full balanced output offers LO
carrier reduction.
The first IF preamplifier has a dB-linear gain adjustment by DC means. Thus, different
ceramic filter losses can be compensated and the overall tuner gain can be adapted to
the individual requirements. The low noise design suppresses post stage noise in the
signal path. Input and output resistance is 330 to support standard ceramic filters. This
is achieved without feedback, which would cause different input impedances when vary-
ing the output impedance.
The second IF preamplifier enables the use of three ceramic filters with real 330 input-
and output termination. Feedthrough of signals is kept low. The high level of output com-
pression is necessary to keep up a high dynamic range.
Beneath the signal path the local oscillator part and the AGC signal generation can be
found on chip. The local oscillator uses the collector grounded colpitts type. A low phase
noise is achieved with this access. A mutual coupling in the oscillator coil is not
necessary.
The AGC Concept
Special care was taken to design a unique AGC concept. It offers 3 AGC loops for differ-
ent kinds of reception conditions. The most important loop is the interference sensor
part.
In today’s high-end car radios, the FM AGC is state of the art. It is necessary to reduce
the influence of 3rd and higher order intermodulation to sustain reception in the pres-
ence of strong signals in the band. On one hand, it makes sense to reduce the desired
signal level by AGC as few as possible to keep up stereo reception, on the other hand
two or more strong out-of-channel signals may interfere and generate an intermodula-
tion signal on the desired frequency. By introducing input attenuation, the level of the
intermod signal decreases by a higher order, whereas the level of the desired signal
shows only a linear dependency on the input attenuation. Therefore, input attenuation
by pin diodes may keep up reception in the presence of strong signals.
The standard solution to generate the pin diode current is to pick up the RF-signal in
front of the mixer. Because the bandwidth at that point is about 1.5 MHz, this is called
wideband AGC. The threshold of AGC start is a critical parameter. A low threshold does
not allow any intermodulation but has the disadvantage of blocking if there is only one
strong station on the band or if the intermod signals do not cover the desired channel. A
higher AGC threshold may tolerate a certain ground floor of intermodulation. This avoids
blocking, but it has the disadvantage, that no reception is possible, if the interfering sig-
nals generate an intermod signal inside the desired channel. This contradiction could
not be overcome in the past.
12 U4065B
4807A–AUDR–05/04

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