ZHCSCX2E January 2014 – October 2017 LM15851
PRODUCTION DATA.
The easiest way to accomplish SE-to-differential conversion for AC-coupled signals is with an appropriate balun.
Figure 32 shows a generic depiction of a SE-to-differential signal conversion using a balun. The circuitry specific to the balun depends on the type of balun selected and the overall board layout. TI recommends that the system designer contact the manufacturer of the selected balun to aid in designing the best performing single-ended to differential conversion circuit using that particular balun.
When selecting a balun, understanding the input architecture of the ADC is important. Specific balun parameters must be considered. The balun must match the impedance of the analog source to the on-chip 100-Ω differential input termination of the LM15851device. The range of this input termination resistor is described in the Electrical Characteristics table as the specification RID.
Also, as a result of the ADC architecture, the phase and amplitude balance are important. The lowest possible phase and amplitude imbalance is desired when selecting a balun. The phase imbalance must be no more than ±2.5° and the amplitude imbalance must be limited to less than 1 dB at the desired input frequency range.
Finally, when selecting a balun, the voltage standing-wave ratio (VSWR), bandwidth, and insertion loss of the balun must also be considered. The VSWR aids in determining the overall transmission line termination capability of the balun when interfacing to the ADC input. The insertion loss must be considered so that the signal at the balun output is within the specified input range of the ADC as described in the Electrical Characteristics table as the specification VID.
Table 1 lists the recommended baluns for specific signal frequency ranges.
MINIMUM FREQUENCY (MHz) | MAXIMUM FREQUENCY (MHz) | IMPEDANCE RATIO | PART NUMBER | MANUFACTURER |
---|---|---|---|---|
4.5 | 3000 | 1:1 | TC1-1-13MA+ | Mini-Circuits |
400 | 3000 | 1:2 | B0430J50100AHF | Anaren |
30 | 1800 | 1:2 | ADTL2-18+ | Mini-Circuits |
10 | 4000 | 1:2 | TCM2-43X+ | Mini-Circuits |