OPA3693 Datasheet, PDF (23/29 Pages) Burr-Brown (TI) – Triple, Ultra-Wideband, Fixed-Gain, VIDEO BUFFER with Disable

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much more voltage-swing-dependent on output
distortion than strictly power-dependent. To use the
500Ω intercept curve, use the single-tone voltage
swing as if it were driving a 50Ω load to compute the
P_O used in the intercept equation.
GAIN ACCURACY AND LINEARITY
The OPA3693 provides improved absolute gain
accuracy and dc linearity over earlier fixed gain of
two line drivers. Operating at a gain of +2V/V by
tying the –IN pin to ground, the OPA3693 shows a
maximum gain error of ±1% at +25°C. The dc gain
therefore lies between 1.98V/V and 2.02V/V at room
temperature. Over the specified temperature ranges,
this gain tolerance expands only slightly due to the
matched temperature drift for R_F and R_G. Achieving
this gain accuracy requires a very low impedance
ground at –IN. Typical production lots show a much
tighter distribution in gain than this ±1% specification.
Figure 55 shows a typical distribution in measured
gain at the gain of +2V/V configuration, in this case
showing a slight drop in the mean (0.25%) from the
nominal but with a very tight distribution.
700
Mean = 1.9883
600
s = 0.0967
500
400
300
200
100
0
Gain (V/V)
Figure 55. Typical +2V/V Gain Distribution
The exceptionally linear output stage (as illustrated
by the high 3rd-order intermodulation intercept) and
low thermal gradient induced errors for the OPA3693
give an extremely linear output over large voltage
swings and heavy loads. Figure 56 shows the tested
deviation (in % of peak-to-peak) from linearity for a
range of symmetrical output swings and loads. Below
4V_PP, for either a 100Ω or a 500Ω load, the
OPA3693 delivers greater than 14-bit linear output
response.
OPA3693
SBOS353 – DECEMBER 2006
0.0200
Figure 42 Test Circuit
0.0175
0.0150
0.0125
0.0100
R_L = 100W
0.0075
0.0050
0.0025
R_L = 500W
0
2
3
4
5
6
7
8
V_O (peak-to-peak)
Figure 56. DC Linearity vs Output Swing and
Loads
NOISE PERFORMANCE
The OPA3693 offers an excellent balance between
voltage and current noise terms to achieve a low
output noise under a variety of operating conditions.
The inverting node noise current (internal) appears at
the output multiplied by the relatively low 300Ω
feedback resistor. The input noise voltage
(1.8nV/√Hz) is extremely low for a unity-gain stable
amplifier. This low input voltage noise was achieved
at the price of higher noninverting input current noise
(17.8pA/√Hz). As long as the ac source impedance
looking out of the noninverting input is less than
100Ω, this current noise does not contribute
significantly to the total output noise. The op amp
input voltage noise and the two input current noise
terms combine to give low output noise for the each
of the three gain settings available using the
OPA3693. Figure 57 shows the op amp noise
analysis model with all of the noise terms included.
In this model, all noise terms are taken to be noise
voltage or current density terms in either nV/√Hz or
pA/√Hz.
E_NI
1/3
OPA3693
E_O
R_S
I_BN
E_RS
4kTR_S
4kT
R_G
R_F
R_G
I_BI
4kTR_F
4kT = 1.6E -20J
at 290K
Figure 57. Op Amp Noise Model
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