THS6212 Datasheet, PDF (28/48 Pages) Texas Instruments – Differential, Line-Driver Amplifier

THS6212
SBOS758 – MAY 2016
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Feature Description (continued)
7.3.5 DC Accuracy and Offset Control
A current-feedback op amp such as the THS6212 provides exceptional bandwidth in high gains, giving fast pulse
settling but only moderate dc accuracy. The Electrical Characteristics tables describe an input offset voltage that
is comparable to high-speed, voltage-feedback amplifiers; however, the two input bias currents are somewhat
higher and are unmatched. Although bias current cancellation techniques are very effective with most voltage-
feedback op amps, these techniques do not generally reduce the output dc offset for wideband current-feedback
op amps. Because the two input bias currents are unrelated in both magnitude and polarity, matching the input
source impedance to reduce error contribution to the output is ineffective. Evaluating the configuration of
Figure 81, using a worst-case condition at 25°C input offset voltage and the two input bias currents, gives a
worst-case output offset range equal to Equation 4:
V_OFF r NG u V_{OS MAX}
§
¨©^IBN
u
R_S
2
u
NG
·
¸¹
r
I_BI u R_F
r 10 u 5 mV 3.5 PA u 25 : u10 r 1.24 k: u 45 PA
r50 mV 0.875 mV r 55.5 mV
V_OFF 104.92 mV to 106.67 mV
where
• NG = noninverting signal gain
(4)
7.4 Device Functional Modes
The THS6212 has four different functional modes set by the BIAS-1 and BIAS-2 pins. Table 1 shows the truth
table for the device mode pin configuration and the associated description of each mode.
BIAS-1
0
1
0
1
BIAS-2
0
0
1
1
Table 1. BIAS-1, BIAS-2 Logic Table
FUNCTION
Full-bias mode (100%)
Mid-bias mode (75%)
Low-bias mode (50%)
Shutdown mode
DESCRIPTION
Amplifiers on with lowest distortion possible (default state)
Amplifiers on with power savings and a reduction in distortion performance
Amplifiers on with enhanced power savings and a reduction of overall
performance
Amplifiers off and output has high impedance
28
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