U2730B-N Datasheet, PDF (6/17 Pages) ATMEL Corporation – L-band Down-converter for DAB Receivers

Overall Properties of the The overall gain of this circuit amounts to 24 dB, the gain-control range is about 30 dB.
Signal Path
With a new AGC concept in the amplifier and mixer, the U2730B-N reaches better inter-
modulation distances (DIM3) at higher IF output power levels.
Power Save Mode
For VPSM > 2 V (pin 1) the power consumption in the analog part (gain-controlled
amplifier and mixer and gain-controlled circuitry) is reduced by 80%. The VCO and the
PLL is not influenced by the power-down mode.
Frequency Synthesizer
The frequency synthesizer block consists of a reference oscillator, a reference divider, a
LO divider in order to divide the frequency of the internal oscillator, a tri-state phase
detector, a lock detector, a programmable charge pump, a loop filter amplifier, a control
interface and a test interface. The control interface is accessed by three control pins, CI,
SI1 and SI2. The test interface provides test signals which represent output signals of
the reference and the LO divider.
The purpose of this unit is to lock the frequency f_VCO of the internal VCO on the fre-
quency f_ref of the reference signal applied to the input pin OSCB phase-locked loop
according to the following relation:
f_VCO = SF ´ f_ref /SF_ref
where: SF = 2464,
SF_ref is the scaling factor of the reference divider according to Table 1
Table 1. Scaling Factors of the Reference Frequency
Voltage at Pin SI1
GND
GND
GND
OPEN
OPEN
OPEN
VCC
VCC
VCC
Voltage at Pin SI2
OPEN
VCC
GND
OPEN
VCC
GND
OPEN
VCC
GND
SF_ref
36
33
48
65
63
64
35
32
49
Reference Oscillator
Frequency
18.432 MHz
–
24.576 MHz
–
–
32.768 MHz
17.920 MHZ
16.384 MHz
–
Reference Oscillator
An on-chip crystal oscillator generates the reference signal which is fed to the reference
divider. By connecting a quartz crystal to pins OSCE and OSCB according to Figure 10,
this oscillator generates a highly stable reference signal. The U2731B (Atmel’s one-chip
front-end IC) offers the reference signal at pin FREF. This reference signal (LC-filtered
to suppress harmonics) can be used to overdrive the oscillator. In this application (see
Figure 11) the reference signal has to be applied to the pin OSCB and the pin OSCE
must be left open.
6 U2730B-N
4719A–DAB–05/03