U2797B Datasheet, PDF (11/13 Pages) TEMIC Semiconductors – 1000-MHz Quadrature Modulator

TELEFUNKEN Semiconductors
U2797B
Application notes
1. Noise floor and settling time
In order to reduce noise on the power down control input
and improve the wide-off noise floor of the 900-MHz RF
output signal, capacitor C_PD should be connected from
pin 8 to ground in the shortest possible way.
The settling time has to be considered for the system un-
m der design. For GSM applications a value of C_PD = 1 F
m defines a settling time, t_sPD, equal or less than 3 s. This
capacitance does not have any influence on the noise floor
within the relevant GSM mask. For mobile application
the mask requirements can be achieved very easily with-
out C_PD.
A significant improvement of the wide-off noise floor is
obtainable with C_PD greater than 100 nF. Such values are
recommended for applications where the settling time is
not critical, such as in base stations. Coupling capacitors
for LO_i and RF_O also have a certain impact on the settling
time. The values used for the measurements are C_LOi =
100 pF and C_RFo = 1 nF.
Mixer input stage
A, B
A, B
94 8187 e
Figure 1 baseband input circuitry
W U2797B-FS ( SSO 20 ) has a 150 k baseband input impedance. The reference voltage, V_REF, is provided at pin 13.
Rev. A1: 06.09.1995
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