OPA2211-EP Datasheet, PDF (20/32 Pages) Texas Instruments – OPA2211-EP 1.1-nV/√Hz Noise, Low-Power, Precision Operational Amplifier

OPA2211-EP
SBOS761 – NOVEMBER 2015
www.ti.com
Typical Application (continued)
8.2.1 Design Requirements
The design requirements for Signal Gain = 11 are:
Signal Gain 1 ^R2
R₁
where
• Supply voltage: 30 V (±15 V)
• R₁ = 100 Ω
• R₂ = 1 kΩ
• R₃ = 11 Ω
(1)
8.2.2 Detailed Design Procedure
8.2.2.1 Total Harmonic Distortion Measurements
OPA2211-EP series operational amplifiers have excellent distortion characteristics. THD + Noise is below
0.0002% (G = +1, VOUT = 3VRMS) throughout the audio frequency range, 20 Hz to 20 kHz, with a 600-Ω load.
The distortion produced by OPA2211-EP series operational amplifiers is below the measurement limit of many
commercially available distortion analyzers. However, a special test circuit illustrated in Figure 47 can be used to
extend the measurement capabilities.
Operational amplifier distortion can be considered an internal error source that can be referred to the input.
Figure 47 shows a circuit that causes the operational amplifier distortion to be 101 times greater than that
normally produced by the operational amplifier. The addition of R3 to the otherwise standard noninverting
amplifier configuration alters the feedback factor or noise gain of the circuit. The closed-loop gain is unchanged,
but the feedback available for error correction is reduced by a factor of 101, thus extending the resolution by 101.
Note that the input signal and load applied to the operational amplifier are the same as with conventional
feedback without R3. The value of R3 should be kept small to minimize its effect on the distortion measurements.
Validity of this technique can be verified by duplicating measurements at high gain and/or high frequency where
the distortion is within the measurement capability of the test equipment. Measurements for this data sheet were
made with an Audio Precision System Two distortion/noise analyzer, which greatly simplifies such repetitive
measurements. The measurement technique can, however, be performed with manual distortion measurement
instruments.
8.2.3 Application Curves
0.001
V_S = 15V
V_OUT = 3V_RMS
Measurement BW = 80kHz
-100
0.0001
G=1
R_L = 600W
G = 11
R_L = 600W
-120
G= 1
R_L = 5kW
0.00001
10
100
1k
Frequency (Hz)
-140
10k 20k
0.1
-60
0.01
0.001
G = 11
-80
-100
0.0001
0.00001
V_S = ±15V G = 1
R_L = 600W
1kHz Signal
Measurement BW = 80kHz
0.000001
0.01
0.1
1
G = -1
10
Output Voltage Amplitude (V_RMS)
-120
-140
-160
100
Figure 43. THD+N Ratio vs Frequency
Figure 44. THD+N Ratio vs Output Voltage Amplitude
20
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