LMH6702 Datasheet, PDF (12/25 Pages) National Semiconductor (TI) – Ultra Low Distortion, Wideband Op Amp

LMH6702
SNOSA03H – NOVEMBER 2002 – REVISED MAY 2016
Feature Description (continued)
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-60
HD2, SOIC
-65
-70
-75
HD2, SOT23
-80
-85
-90
-95
-100
HD3, SOIC
HD3, SOT23
-105
-110
1
10
100
Frequency (MHz)
Figure 23. SOIC and SOT-23 Packages Distortion Terms Compared
The LMH6702 data sheet shows both SOT-23 and SOIC data in Electrical Characteristics to aid in selecting the
right package. Typical Characteristics shows SOIC package plots only.
7.3 Device Functional Modes
7.3.1 2-Tone 3^rd Order Intermodulation
Figure 10 shows a relatively constant difference between the test power level and the spurious level with the
difference depending on frequency. The LMH6702 does not show an intercept type performance, (where the
relative spurious levels change at a 2X rate versus the test tone powers), due to an internal full power bandwidth
enhancement circuit that boosts the performance as the output swing increases while dissipating negligible
quiescent power under low output power conditions. This feature enhances the distortion performance and full
power bandwidth to match that of much higher quiescent supply current parts.
7.3.2 DC Accuracy and Noise
The example in Equation 1 shows the output offset computation equation for the non-inverting configuration
using the typical bias current and offset specifications for A_V = 2:
Output Offset:
V_O = (±I_BN · R_IN ± V_IO) (1 + R_F/R_G) ± I_BI · R_F
where
• R_IN is the equivalent input impedance on the non-inverting input.
(1)
Example computation for A_V = +2, R_F = 237Ω, R_IN = 25Ω:
V_O = (±6 μA × 25 Ω ± 1mV) (1 + 237/237) ± 8 μA × 237 = ±4.20 mV
(2)
A good design, however, should include a worst case calculation using min/max numbers in the data sheet
tables, in order to ensure worst case operation.
Further improvement in the output offset voltage and drift is possible using the composite amplifiers described in
Application Note OA--07, Current Feedback Op Amp Applications Circuit Guide (SNOA365). The two input bias
currents are physically unrelated in both magnitude and polarity for the current feedback topology. It is not
possible, therefore, to cancel their effects by matching the source impedance for the two inputs (as is commonly
done for matched input bias current devices).
The total output noise is computed in a similar fashion to the output offset voltage. Using the input noise voltage
and the two input noise currents, the output noise is developed through the same gain equations for each term
but combined as the square root of the sum of squared contributing elements. See Application Note OA-12,
Noise Analysis for Comlinear Amplifiers (SNOA375) for a full discussion of noise calculations for current
feedback amplifiers.
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