U4256BM Datasheet, PDF (10/14 Pages) TEMIC Semiconductors – Frequency Synthesizer for Radio Tuning

U4256BM
OSCIN, OSCOUT
A crystal resonator (up to 16 Mhz) is connected between
OSCIN and OSCOUT in order to generate the reference
frequency. The complete application circuit is shown in
figure 15. If a reference is available, it can be applied at
OSCIN. The minimum voltage should be 100mVrms. In
this case, pin OSCOUT has to be open.
V_DD
OSCIN
V_DD
OSCOUT
Figure 11.
14865
Application Information
Function of DAC1, 2 in the FM Mode
For automatic tuner alignment, the DAC1 and 2 of the
U4256BM can be controlled by setting gain and offset
values. The following figure shows the principle of the
operation in FM mode. The gain is in the range of
0.7 to 2.15. The offset range is +0.5 V to –0.6 V. For
alignment, DAC1 and 2 are connected to the varicaps of
the preselection filter and the IF filter. For alignment,
offset and gain is set for having the best tuner tracking
Function of DAC1, 2 in the AM Mode
In AM mode, DAC1, 2 can be used as standard DAC
converters. The resolution of 8 bit is controlled via the
gain bits in a range of approximately 0.5 V to 7 V,
depending on the offset value.
FMOSCIN Sensitivity
W Vi (mV_rms on 50 )
150
PDO _Gain
+/– ^DAC1,2
Offset
14907
Figure 12.
100
50
0
0 20 40 60 80 100 120 140 160
Frequency (MHz)
Figure 13.
10 (14)
Preliminary Information
Rev. A2, 03-Nov-98