“Differential drivers can be driven by single-ended or differential signals, and today we will analyze both cases using unterminated or terminated signal sources. Figure 1 shows a differential driver driven by a balanced unterminated signal source. This is usually the case for low-impedance signal sources, where the connection distance between the source and the driver is very short.

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Differential drivers can be driven by single-ended or differential signals, and today we will analyze both cases using unterminated or terminated signal sources.

**01 Differential input, unterminated signal source**

Figure 1 shows a differential driver driven by a balanced unterminated signal source. This is usually the case for low-impedance signal sources, where the connection distance between the source and the driver is very short.

Figure 1: Differential Input, Unterminated Signal Source

The design input is the source impedance R_{S}Gain setting resistor R_{G1}and the desired gain G. Note: The gain is relative to the signal voltage source V_{SIG}Take measurements.

with respect to the signal source V_{SIG}the total value of the gain setting resistors is equal to R_{G1}+R_{S}/2. In addition, R_{G2}=R_{G1}. Thus, the desired feedback resistor value (R_{F1}=R_{F2}) can be calculated by the following formula:

**02 Differential input, termination signal source**

In many cases, a differential drive source needs to drive twisted pairs, which must be terminated to their characteristic impedance in order to maintain high bandwidth and minimize reflections, as shown in Figure 2.

Figure 2. Differential Input, Terminated Signal Source

The design input is the source impedance R_{S}Gain setting resistor R_{G1}and the desired gain G. Note: For the termination case, the gain is the differential voltage with respect to the termination resistor (V_{IN}=V_{D}+CV_{D-}) to measure.

For balanced differential drive, the input impedance R_{IN}equal to 2R_{G1}. Termination resistor R_{T}Choose according to the following conditions: R_{T }|| R_{IN }=R_{S}_{,}or

Thus, the desired feedback resistor value (R_{F1}=R_{F2}) can be calculated by the following formula:

**03 Single-ended input, unterminated signal source**

In many applications, differential amplifiers provide an efficient way to convert single-ended signals to differential signals. Figure 3 shows the case of an unterminated single-ended driver.

Figure 3. Single-ended input, unterminated signal source

The design input is the source impedance R_{S}Gain setting resistor R_{G1}and the desired gain G. Note: The gain is relative to the signal voltage source V_{SIG}Take measurements.

To prevent V_{OCM}To produce a bad offset voltage at the differential output, the net impedance seen by the two inputs of the differential amplifier must be equal. therefore,

In this way, the feedback resistor value can be calculated by:

**04 Single-ended input, terminated signal source**

Figure 4 shows a very common application where a single-ended signal source drives a coaxial cable; to minimize reflections and maintain high bandwidth, the coaxial cable must be properly terminated.

The design input is the source impedance R_{S}Gain setting resistor R_{G1}and the desired gain G. Note: The gain is relative to the voltage of the termination resistor, V_{IN}Take measurements.

Figure 4. Single-ended input, terminated signal source

Know the desired gain G, gain setting resistor R_{G1}and signal source resistance R_{S}, calculate the initial value of the feedback resistor RF1A. The final value of this resistor will be slightly higher due to the need to increase R_{G2}to match the input impedance, which will be calculated by the formula below. The calculation process is as follows:

Input voltage V_{IN}with the signal source voltage V_{SIG}Has the following relationship:

To calculate the final value of the feedback resistor, use the Thevenin equivalent circuit shown in Figure 5.

Figure 5. Thevenin Equivalent Input Circuit

The output voltage can be expressed as a function of the source voltage:

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