THS3215 Datasheet, PDF (25/71 Pages) Texas Instruments – THS3215 650-MHz, Differential to Single-Ended DAC Output Amplifier

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THS3215
SBOS780A – MARCH 2016 – REVISED APRIL 2016
8.4 Noise Measurement
All the noise measurements were made using the very low-noise, high-gain bandwidth LMH6629 as a low-noise
preamplifier to boost the output noise from the THS3215 before measurement on a spectrum analyzer, as shown
in Figure 72. The 0.69-nV/√Hz input-voltage noise specification of the LMH6629 provides flat gain of 20 V/V
through 100 MHz with its ultrahigh, 6.3-GHz gain bandwidth product. The D2S and OPS noise was measured
with the common-mode voltage at GND.
I Input
Q Input
Spectrum
Analyzer
Ext Trig
RF
Input
50
THS3215EVM
+
±
LMH6629
Noise Preamp
+
±
Figure 72. Noise Measurement Using LMH6629 Preamplifier
8.5 Output Impedance Measurement
Output impedance measurement for the three stages under different conditions were performed as a small-signal
measurement calibrated to the device pins using an impedance analyzer. Calibrating the measurement to the
device pins removes the THS3215EVM parasitic resistance, inductance, and capacitance from the measured
data.
8.6 Step-Response Measurement
Generating a clean, fast, differential-input step for time-domain testing presents a considerable challenge. A
multichannel pulse generator with adjustable rise and fall times was used to generate the differential pulse to
drive D2S inputs in Figure 21. A high-speed scope was used to digitize the pulse response.
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