THS4520_14 Datasheet, PDF (25/37 Pages) Texas Instruments – WIDEBAND, LOW NOISE, LOW DISTORTION FULLY DIFFERENTIAL AMPLIFIER

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particular interest because their joint interaction
reflects the usable slewing and bandwidth limits of a
device. Output swing and frequency limits are often
prime consideration when picking a device and
quantifying their joint impact on HD allows a more
precise judgment on the ability of a device to meet
the need for speed. The curves that separate each
colored region represent the value of HD2,3
indicated on the plot. Following a curve over the
ranges of output swing and frequency show the
conditions over which that value of HD2,3 occurs.
Note that the horizontal axis represents the base-10
logarithm of frequency in units of MHz. So on the
horizontal axis the value of ‘2’ represents 100 MHz,
‘1’ represents 10 MHz and ‘0’ represents 1 MHz,
respectively. This strategy was chosen to provide
spacing between curves that allowed the viewer to
easily resolve the individual curves. Plotting
frequency on a linear scale caused the curves to be
crowded and difficult to distinguish. Unfortunately a
semilog axis format was not possible because of the
plotting function. The measured data in the plots
THS4520
SLOS503B – SEPTEMBER 2006 – REVISED JULY 2007
represent measurements of a THS4520 evaluation
board in the default unity-gain configuration with R_L =
200Ω. For more information on the circuit
configuration, see the information on the THS4520
evaluation board later in this section.
The first two plots (Figure 67 andFigure 68) are for
HD2 and HD3 respectively, with a power supply of
±2.5 V. The line labeled Large Signal BW in each of
the two plots represents the measured large signal
bandwidth over the range of output signal swing in
the plot (V_out = 1 V_pp to 8 V_pp). The BW lines fall in
the shaded region that represents very poor
distortion performance: HD2 > –45dBc or HD3 >
–40dBc. The intent in plotting the bandwidth was to
provide a realistic comparison between the reported
large signal bandwidth and useful distortion
performance. The areas between the plots are
shaded to help illustrate the 10dB changes in HD2 or
HD3 between the adjacent curves. The third and
fourth plots (Figure 69andFigure 70) are the constant
contours of HD2 and HD3 respectively for a power
supply of ±1.65 V.
Figure 67. Constant HD2 Contours vs Output Swing and log₁₀ (Frequency - MHz)
V_s = 2.5 V, Gain = 1, R_L = 200 Ω
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