SBOS778D April   2016  – April 2021

PRODUCTION DATA

1. Features
2. Applications
3. Description
4. Revision History
5. Companion Devices
6. Pin Configuration and Functions
7. Specifications
8. Parameter Measurement Information
9. Detailed Description
10. 10Application and Implementation
1. 10.1 Application Information
2. 10.2 Typical Applications
1. 10.2.1 An MFB Filter Driving an ADC Application
2. 10.2.2 Differential Transimpedance Output to a High-Grade Audio PCM DAC Application
3. 10.2.3 ADC3k Driver with a 2nd-Order RLC Interstage Filter Application
11. 11Power Supply Recommendations
12. 12Layout
1. 12.1 Layout Guidelines
2. 12.2 Layout Example
3. 12.3 EVM Board
13. 13Device and Documentation Support
14. 14Mechanical, Packaging, and Orderable Information

• RUN|10
• DGK|8
• RGT|16
• RUN|10
• DGK|8
• RGT|16

### 10.1.1 Noise Analysis

The first step in the output noise analysis is to reduce the application circuit to the simplest form with equal feedback and gain setting elements to ground. Figure 10-1 shows the simplest analysis circuit with the FDA and resistor noise terms to be considered.

Figure 10-1 FDA Noise Analysis Circuit

The noise powers are shown in Figure 10-1 for each term. When the RF and RG (or RI) terms are matched on each side, the total differential output noise is the root sum squared (RSS) of these separate terms. Using NG ≡ 1 + RF / RG, the total output noise is given by Equation 10. Each resistor noise term is a 4kT × R power (4kT = 1.6E-20J at 290K).

Equation 10.

The first term is simply the differential input spot noise times the noise gain, the second term is the input current noise terms times the feedback resistor (and because there are two uncorrelated current noise terms, the power is two times one of them), and the last term is the output noise resulting from both the RF and RG resistors, at again twice the value for the output noise power of each side added together. Running a wide sweep of gains when holding RF close to 1 kΩ and setting the input up for a 50-Ω match gives the standard values and resulting noise listed in Table 10-1.

Note that when the gain increases, the input-referred noise approaches only the gain of the FDA input voltage noise term at 3.3 nV/√ Hz.

Table 10-1 Swept Gain of the Output- and Input-Referred Spot Noise Calculations
GAIN (V/V)RFRG1RTRG2ZINAVEO (nV/√ Hz)EI (nV/√ Hz)
0.110001000049.91000049.660.09965770
1100097651.1100049.21.009610.410.4
2102049952.352348.91.98813.96.95
510001875921550.25.057234.6
10102088.769.811850.610.0936.43.64