LMH6551Q-Q1 Datasheet, PDF (14/25 Pages) National Semiconductor (TI) – LMH6551Q Differential, High Speed Op Amp

LMH6551Q
SNOSB95E – NOVEMBER 2011 – REVISED MARCH 2013
www.ti.com
SINGLE ENDED INPUT TO DIFFERENTIAL OUTPUT
The LMH6551Q provides excellent performance as an active balun transformer. Figure 30 shows a typical
application where an LMH6551Q is used to produce a differential signal from a single ended source.
In single ended input operation the output common mode voltage is set by the V_CM pin as in fully differential
mode. Also, in this mode the common mode feedback circuit must recreate the signal that is not present on the
unused differential input pin. Figure 25 is the measurement of the effectiveness of this process. The common
mode feedback circuit is responsible for ensuring balanced output with a single ended input. Balance error is
defined as the amount of input signal that couples into the output common mode. It is measured as a the
undesired output common mode swing divided by the signal on the input. Balance error can be caused by either
a channel to channel gain error, or phase error. Either condition will produce a common mode shift. Figure 25
measures the balance error with a single ended input as that is the most demanding mode of operation for the
amplifier.
Supply and V_CM pin bypassing are also critical in this mode of operation. See the above section on FULLY
DIFFERENTIAL OPERATION for bypassing recommendations and also see Figure 28 and Figure 29 for
recommended supply bypassing configurations.
Figure 30. Single Ended In to Differential Out
14
Submit Documentation Feedback
Product Folder Links: LMH6551Q
Copyright © 2011–2013, Texas Instruments Incorporated