RF133 Conexant Systems, Inc., RF133 Datasheet - Page 4

• Manufacturer Part Number: RF133
• Manufacturer: Conexant Systems, Inc.

PGA has two gain settings, either 0 dB or 20 dB, whereas both
PGB and PGC have a gain range of -10 dB to 20 dB
programmable in 2 dB steps. The output of PGC is fed to a
quadrature mixer. The quadrature mixer has a fixed conversion
gain of 10 dB and its LO inputs are taken from the outputs of a
quadrature divider (divide by 2 or 4).
Baseband Integrated Filters, Baseband Amplifiers, and DC
Offset Compensation. Immediately following the quadrature
mixer (demodulator) is the baseband section (DC offset
compensation circuitry, two integrated baseband filters and two
programmable gain amplifiers). Each programmable gain
amplifier in the baseband section, both labelled PGD, has four
different gain settings: 0 dB, 10 dB, 20 dB, or 30 dB.
The corner frequency of the integrated baseband filters is
adjustable by using an appropriate value resistor at pin 26,
LPFADJ. At the nominal cutoff frequency of 105 kHz, the
resistor value is 75.1 k .
Due to possible high gain of the baseband amplifiers (PGD), any
DC offsets at the outputs of the quadrature mixer are amplified
and, if uncorrected, the I and Q outputs can suffer from
significant unwanted DC offset voltages. To cancel out these
effects, the RF133 must be calibrated.
4
October 8, 1999
Antenna
Coupler
Diplexer
T/R
T/R
VAPC
Rx Filter
Rx Filter
RF142
DCS
GSM
LNA/Image Reject Mixer
Tx/Rx VCO
RM008
RF210
Proprietary Information and Specifications are Subject to Change
Figure 3. Dual-Band Transceiver Chipset Using The RF133
C o m b i n e r
UHF VCO
TX DCS VCO
TX GSM VCO
D U A L P L L
LOOP FILTER
Conexant
IF SAW
Tx/Rx VCO
Filter
During compensation, the correction voltages are stored in
external hold capacitors CTH1 and CTH2, then the loop is
opened immediately thereafter. The corrected I and Q outputs
are then fed directly to external circuitry for further baseband
processing.
The timing diagram for this calibration sequence in reference to
the receive slot is shown in Figure 4 (the front-end mixer is
assumed to be Rockwell’s RF210 dual-band, image reject
downconverter). At first, the RF133 receiver is turned on
(RXENA is high). After time T1, the track and hold signal, T/H,
places the DC compensation circuitry in the track mode for time
T2. Then, there is a settling time, T3, before the external front-
end is turned on. Finally, the front-end must be turned on for
time T4 before the receive slot.
Time T2 can vary from 10 sec to 350 sec. This duration is
dependent on 1) the value of the hold capacitors (CTH1 and
CTH2), and 2) whether the calibration is done from frame to
frame or from a cold start. This is tabulated in Table 2.
P G A
P G B
P G C
LC
Tank
C H P
÷2 ÷4
÷2 ÷4
P F D
÷1 ÷2
90
˚
÷2 ÷4
÷1 ÷2
TX IF FILTER
Control
3 Wire
RF133
P G D
P G D
90
˚
Bias
D C
O C
L P F
L P F
C453
RXI
C L K
R X Q
S X E N A
R X E N A
T X E N A
D A T A
L E
TXI
T X Q
T / H
100776A
CTH1
CTH2