ATR2731-ILQY Atmel, ATR2731-ILQY Datasheet - Page 9

• Manufacturer Part Number: ATR2731-ILQY
• Description: IC DAB ONE-CHIP FRONT END 44SSOP
• Manufacturer: Atmel

Specifications of ATR2731-ILQY

• Rf Type: DAB, Broadcast Radio
• Frequency: 70MHz ~ 260MHz
• Features: 8.5V Supply Voltage
• Package / Case: 44-SSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

6. PLL Part
6.1
4904A–DAB–03/06
Reference Oscillator
The purpose of the PLL part is to perform a phase lock of the voltage-controlled RF oscillator to
a n o n - c h i p c r y s t a l r e f e r e n c e o sc i l l a t o r . T h i s i s a c h i e v e d b y m e a n s o f a s p e c i a l
phase-noise-shaping technique based on the fractional-N principle. It concentrates the phase
detector's phase-noise contribution to the spectrum of the controlled VCO at frequency positions
where it does not impair the quality of the received DAB signal. A special property of the trans-
mission technique used in DAB is that the phase-noise-weighting function measuring the
influence of the LO's phase noise on the phase information of the coded signal in a DAB receiver
has zeros; that is, if phase noise is concentrated in the position of such zeros as discrete lines,
the DAB signal is not impaired as long as these lines do not exceed a set limit. For DAB mode I,
this phase-noise- weighting function is shown in
Figure 6-1.
It is important to realize that this function shows zeros in all distances from the center line which
are multiples of the carrier spacing. The technique of concentrating the phase noise in the posi-
tions of such zeros is patent protected.
An on-chip crystal oscillator generates the reference signal which is fed to the reference divider.
As already described in
nal for the mixer in the IF section is derived. By applying a crystal to the pins OSCI and OSCO
(Figure 13-2 on page
reference signal is available, the oscillator can be used as an input buffer. In such an application
(Figure 13-3 on page
OSCO must be left open.
Phase-noise-weighting Function
21), this oscillator generates a highly stable reference signal. If an external
22), the reference signal has to be applied to the pin OSCI and the pin
“IF Gain-controlled Amplifier/Mixer Combination” on page
1,40
1,20
1,00
0,80
0,60
0,40
0,20
0,00
1,60
1,80
0
1000
2000
3000 4000
df/Hz
Figure
5000 6000
6-1.
7000 8000
9000 10000
ATR2731
8, the LO sig-
9