Rainbow Electronics MAX3541 - Manual (Page 16)

MAX3541
Application Information
RF Inputs
The MAX3541 features separate UHF and VHF inputs
that are matched to 75Ω. Both inputs require a DC-
blocking capacitor. The active inputs are selected by
the input registers. In addition, the input registers
enable or disable the lowpass filter, which can be used
when the VHF input is selected. For the 47MHz to
68MHz, select the VHF_IN with the LPF filter enabled
(INPT = 00). For 174MHz to 230MHz, select VHF_IN
with LPF disabled (INPT = 01). For 470MHz to 862MHz,
select UHF_IN (INPT = 10).
RF Gain Control
The gain of the RF low-noise amplifier can be adjusted
over a typical range of 45dB with the RFAGC pin. The
RFAGC input accepts a DC voltage from 0.5V to 3V,
with 3V providing maximum gain. This pin can be con-
trolled with the IF power-detector output to form a
closed RF gain-control loop. See the
Closed-Loop RF
Gain Control section for more information.
RF Tracking Filter
The MAX3541 includes a programmable tracking filter
for each band of operation to optimize rejection of
out-of-band interference while minimizing insertion
loss for the desired received signal. The center fre-
quency of each tracking filter is selected by a
switched-capacitor array that is programmed by the
TFS[7:0] bits in the Tracking Filter Series Capacitor
register and the TFP[5:0] bits in the Tracking Filter
Parallel Cap register.
Optimal tracking filter settings for each channel varies
from part to part due to process variations. To accom-
modate part-to-part variations, each part is factory cal-
ibrated by Maxim. During calibration, the y-intercept
and slope for the series and parallel tracking capacitor
arrays is calculated and written into an internal ROM
table. The user must read the ROM table upon power-
up and store the data in local memory (8 bytes total) to
calculate the optimal TFS[7:0] and TFP[5:0] settings
for each channel. Table 16 shows the address and
bits for each ROM table entry. See the
Interpolating
Tracking Filter Coefficients section for more informa-
tion on how to calculate the required values.
Reading the ROM Table
Each ROM table entry must be read using a two-step
process. First, the address of the ROM bits to be read
must be programmed into the TFA[3:0] bits in the
Tracking Filter ROM Address register (Table 11).
Complete Single-Conversion
Television Tuner
16 ______________________________________________________________________________________
MSB LSB
DATA BYTE DESCRIPTION ADDRESS
D7 D6 D5 D4 D3 D2 D1 D0
Reserved 0x0 OD2 OD1 OD0 X X X X X
VHF Series
Y-Intercept
0x1 VS0[7] VS0[6] VS0[5] VS0[4] VS0[3] VS0[2] VS0[1] VS0[0]
VHF Series
Slope
0x2 VS1[7] VS1[6] VS1[5] VS1[4] VS1[3] VS1[2] VS1[1] VS1[0]
VHF Parallel
Y-Intercept
0x3 VP0[7] VP0[6] VP0[5] VP0[4] VP0[3] VP0[2] VP0[1] VP0[0]
VHF Parallel
Slope
0x4 VP1[7] VP1[6] VP1[5] VP1[4] VP1[3] VP1[2] VP1[1] VP1[0]
UHF Series
Y-Intercept
0x5 US0[7] US0[6] US0[5] US0[4] US0[3] US0[2] US0[1] US0[0]
UHF Series
Slope
0x6 US1[7] US1[6] US1[5] US1[4] US1[3] US1[2] US1[1] US1[0]
UHF Parallel
Y-Intercept
0x7 UP0[7] UP0[6] UP0[5] UP0[4] UP0[3] UP0[2] UP0[1] UP0[0]
UHF Parallel
Slope
0x8 UP1[7] UP1[6] UP1[5] UP1[4] UP1[3] UP1[2] UP1[1] UP1[0]
Table 16. ROM Table