U4256BM-R Datasheet, PDF (5/19 Pages) ATMEL Corporation – Frequency Synthesizer for Radio Tuning

U4256BM-R
Function of DAC1, 2 in
FM and AM Mode
(Pin 3 and Pin 4)
For automatic tuner alignment, the DAC1 and DAC2 of the U4256BM-R can be con-
trolled by setting gain of VPDO and offset values. The following figure shows the
principle of the operation. In FM Mode the gain is in the range of 0.69 × V_(PDO) to 2.16 ×
V_(PDO). The offset range is +0.56 V to -0.59 V. For alignment, DAC1 and DAC2 are con-
nected to the varicaps of the preselection filters. For alignment, offset and gain is set for
having the best tuner tracking.
Figure 6. Principle Operation for Alignment
Bit 34
PDO (FM)
Gain
DAC1,2
+/-
Vref (AM)
(3 V)
Offset
The DAC mode can be controlled by setting the Bit 34 as following:
DAC Mode
B34
FM
0
AM
1
If Bit 34 = 1 (AM Mode), the DAC1, DAC2 can be used as standard DAC converters.
The internal voltage of 3 V is connected to the gain- and offset-input of DAC1 and DAC2
(only in AM Mode). The gain is in the range of 0.46 × 3 V to 3.03 × 3 V. The offset range
is +1.46 V to -1.49 V.
Figure 7. Internal Components at DAC1,2 Output
VS
DAC1,2
5
4562C–AUDR–08/04