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LMH6552

www.ti.com

SNOSAX9I – APRIL 2007 – REVISED JANUARY 2015

9.2.2 Single-Ended Input to Differential Output Operation

In many applications, it is required to drive a differential input ADC from a single-ended source. Traditionally,

transformers have been used to provide single to differential conversion, but these are inherently bandpass by

nature and cannot be used for DC coupled applications. The LMH6552 provides excellent performance as a

single-to-differential converter down to DC. Figure 45 shows a typical application circuit where an LMH6552 is

used to produce a differential signal from a single-ended source.

Figure 45. Single-Ended Input with Differential Output

When using the LMH6552 in single-to-differential mode, the complementary output is forced to a phase inverted

replica of the driven output by the common mode feedback circuit as opposed to being driven by its own

complimentary input. Consequently, as the driven input changes, the common mode feedback action results in a

varying common mode voltage at the amplifier's inputs, proportional to the driving signal. Due to the non-ideal

common mode rejection of the amplifier's input stage, a small common mode signal appears at the outputs which

is superimposed on the differential output signal. The ratio of the change in output common mode voltage to

output differential voltage is commonly referred to as output balance error. The output balance error response of

the LMH6552 over frequency is shown in Typical Performance Characteristics.

These equations, along with the source matching condition, must be solved iteratively to achieve the desired gain

with the proper input termination. Component values for several common gain configurations in a 50-

Ω

9.2.3 Single Supply Operation

Single supply operation is possible on supplies from 5 V to 10 V; however, as discussed earlier, AC input

coupling is recommended for low supplies such as 5 V due to input common mode limitations. An example of an

AC coupled, single supply, single-to-differential circuit is shown in Figure 46. Note that when AC coupling, both

inputs need to be AC coupled irrespective of single-to-differential or differential-to-differential configuration. For

higher supply voltages DC coupling of the inputs may be possible provided that the output common mode DC

level is set high enough so that the amplifier's inputs and outputs are within their specified operating ranges.

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