U2896B Datasheet, PDF (9/13 Pages) TEMIC Semiconductors – Modulation PLL for GSM, DCS and PCS Systems

U2896B
Application Hints
Interfacing
For some of the baseband ICs it may be necessary to
reduce the I/Q voltage swing so that it can be handled by
the U2896B. In those cases, the following circuitry can be
used.
Mode Control
U2896B
U2896B
I
NI
Baseband IC
Q
NQ
R1
I
R1 ^{R2 C}
NI
U2896B
Q
R1
C
R2
NQ
R1
14901
Figure 11. Interfacing the U2896B to I/Q baseband circuits
Due to a possible current offset in the differential base-
band inputs of the U2896B the best values for the carrier
suppression of the I/Q modulator can be achieved with
v W ^{voltage driven I/NI-, and Q/NQ-inputs. A value of}
R_source = R2/2*R_S 1.5 k should be realized. R_S is the
sum of R1 (above drawing) and the output resistance of
the baseband IC.
VS2
VS2
R_Mode
MC
R_Mode1 R_Mode2
MC
a) any single mode b) any 2 modes
U2896B
VS2
R_Mode
MC
c) any mode
& mode 5
U2896B
VS2
R_Mode
MC
36 kΩ or
10 kΩ
d) mode 5 & mode 3 or mode 4
14895
Figure 12. Application examples for programming
different modes
Rev. A1, 18-Sep-98
9 (13)
Preliminary Information