3-141
RF3330
Rev A4 060908
Evaluation Test Procedure
Introduction
The RF3330 is an IF amplifier with AGC, designed for
use in Cable Television applications. Voltage gain is
varied using an analog voltage control signal. The dif-
ferential input is high impedance (2000
Ω) and the dif-
ferential output is low impedance (10
Ω). The 3dB
bandwidth is 150MHz and has a maximum voltage
gain of 34dB and a minimum voltage gain of 8dB. The
AGC Control Voltage ranges from 0.5V for minimum
gain to 3.3V for maximum gain. The device is pack-
aged in the SOT23-8, which minimizes board area.
Evaluation Board
The 3330410 board has been designed to achieve
maximum versatility for device evaluation. The board is
designed for either a differential or single-ended input
signal. Likewise, the output can be either singly or dif-
ferentially loaded. There is also a separate VCC and
AGC voltage pin. For constant maximum gain applica-
tions, the VCC and AGC pins can be tied together.
Input
For differential operation on the input, the J1 connector
(VIN unbalanced) is not required. Differential voltages
are applied directly through connectors J2 and J3 (VIN
balanced). DC blocking capacitors are also provided to
protect equipment or upstream components. Boards
ordered from RF Micro Devices are assembled in this
configuration.
Single-ended operation on the input can be accom-
plished in two ways. The first option uses the differen-
tial board setup as described above, with the addition
of an external low frequency 180° power combiner.
The combiner splits the single input signal into two sig-
nals with inverted phase. The second option for single-
ended operation utilizes a SAW filter which converts
from double to single-ended. The current evaluation
board has an option to insert a SAW filter on the input.
For this setup, the J1 connector (VIN unbalanced)
would be utilized. The 3330410 board has been evalu-
ated using a 44MHz Siemens+Matsushita filter. This is
a common IF frequency used in cable modem applica-
tions.
Output
For differential operation on the output, the optional
C4, C5, R1, and R5 would be inserted and the T1
transformer would be removed. The J4 (VOUT unbal-
anced) and J5 (VOUT balanced) connectors would be
uses as differential outputs.
For single-ended operation on the output, only the J4
connector (VOUT unbalanced) is used and only one
analyzer is necessary. There is a 1:1 transformer to
convert the unbalanced output to a balanced signal.
The amplifier is designed to drive a 1000
Ω load. Driv-
ing a 50
Ω load, presented by the spectrum analyzer
will cause the amplifier to saturate. In order to present
a 1000
Ω load to the amplifier a resistive matching cir-
cuit is on the board. Boards ordered from RF Micro
Devices are assembled in this configuration.
Test Setup Calibration
Because of the fact that the impedances of the ampli-
fier are not 50
Ω, there are some special considerations
when calibrating a test setup.The evaluation test setup
is shown in Figure 1.
Input
As stated previously, the balanced input impedance of
the RF3330 is 2000
Ω. The signal generator used has
an unbalanced 50
Ω source, and is typically used in
unbalanced 50
Ω impedance systems. Due to this load
mismatch, a positive amplitude offset needs to be
applied to the signal generator. The formulas used to
calculate this offset are given below in Equations 1
through 3. It should be noted that the unbalanced
1000
Ω load is used, because all data in the datasheet
is referenced to single-ended operation. Using a spec-
trum analyzer probe, the actual offset measured was
7.5dB, and this is what is used for the amplitude offset
in the signal generator.
Mismatch Loss (ML)=-10*log(1-|
Γ
L|
2)Eq. 1
Γ
L =(Z - Z0)/(Z +Z0)Eq. 2
ML=-10*log(1-[(1000-50)/(1000+50)]2)=7.4dB
Eq. 3
Table 1. SAW Filters
EPCOS P/N
FC (MHz)
X6857D
36.000
X6966M
36.125
X6964D
43.750
X6855M
44.000
X6866D
44.000
X6965M
44.000
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