Datasheet

-65
-60
-55
-50
-45
-40
-35
-30
1 10 100
HD2
HD3
f-Frequency-MHz
Gain-dB
8 Initial Power Up and Test
8.1 Initial Test
8.2 Functional Test
9 Optional Configurations
9.1 Optional OPA656 Input Buffer
Initial Power Up and Test www.ti.com
Figure 13. Harmonic Distortion for TSW7001 in 40-dB Gain Mode
Plug in the 6-V power supply. This lights up the power LED D18.
Plug in the USB cable, and connect it to the PC. Allow a few seconds for the USB to register and
enumerate. Once the computer has detected the TSW7001 EVM, then start the TSW7001 Control Panel
GUI – refer to Section 5 . Ensure that the TSW7001 Control Panel GUI connects to the TSW7001 EVM.
Do not connect any input signals into J26 at this time. Change the static voltage register value in the GUI
to 0, and click WRITE. Monitor the voltage level at C74. This level reads –1 V. Change the static register
value to 65535, click WRITE. This generates a +1 V on C74. This is the range of the control voltage used
to control the gain of the VCA824. Set the register value back to 0 (–1 V for minimum gain).
Connect a 50- Ω signal source to the input of the TSW7001EVM at J26. Set the signal frequency to 10
MHz, and the amplitude to -20 dBm.
Set the static voltage register value to 32767 (midscale) to set the control voltage to about 0 Vdc. Verify at
the output SMA J27 that the 10-MHz tone changes to 20 dB.
Verify that the cyclic step and ramp functions on the first tab of the GUI by entering values for the step and
ramp. Monitor on an oscilloscope that the sine-wave amplitude is changing as expected.
Verify that the arbitrary cyclic function on the second tab of the GUI by entering some arbitrary gain steps.
An OPA656 amplifier is included on the EVM to be used as an input buffer stage. The OPA656 combines
a wideband, unity-gain-stable, voltage-feedback operational amplifier with a FET-input stage to offer an
ultra-high, dynamic-range amplifier for buffering and transimpedance applications. Extremely low dc errors
give good precision in optical applications.
14 Voltage-Controlled Amplifier Evaluation Kit SLWU058 – August 2008
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