ADA4830-1/ADA4830-2

Data Sheet

Rev. C | Page 14 of 22

APPLICATIONS INFORMATION

METHODS OF TRANSMISSION

Pseudo Differential Mode (Unbalanced Source

Termination)

The ADA4830-1 and ADA4830-2 can be operated in a pseudo

differential configuration with an unbalanced input signal. This

allows the receiver to be driven by a single-ended source. Pseudo

differential mode uses a single conductor to carry an unbalanced

signal and connects the negative input terminal to the ground

reference of the source.

Use the positive wire or coaxial center conductor to connect the

source output to the positive input (INP) of the ADA4830-1 or

ADA4830-2. Next, connect the negative wire or coaxial shield from

the negative input (INN) back to a ground reference on the source

printed circuit board (PCB). The input termination should match

the source impedance and be referenced to the remote ground.

An example of this configuration is shown in Figure 30.

INN

INP

ADA4830-1

75

Ω

−

+

75

Ω

POSITIVE WIRE

NEGATIVE WIRE

DRIVER PCB

SINGLE-ENDED

AMPLIFIER

Figure 30. Pseudo Differential Mode

Pseudo Differential Mode (Balanced Source Impedance)

Pseudo differential signaling is typically implemented using

unbalanced source termination, as shown in Figure 30. With

this arrangement, however, common-mode signals on the

positive and negative inputs receive different attenuation due to

unbalanced termination at the source. This effectively converts

some of the common-mode signal into differential mode signal,

degrading the overall common-mode rejection of the system.

System common-mode rejection can be improved by balancing

the output impedance of the driver, as shown in Figure 31.

Splitting the source termination resistance evenly between the

hot and cold conductors results in matched attenuation of the

common-mode signals, ensuring maximum rejection.

INN

INP

ADA4830-1

75

Ω

−

+

37.5

Ω

37.5

Ω

POSITIVE WIRE

NEGATIVE WIRE

DRIVER PCB

SINGLE-ENDED

AMPLIFIER

Figure 31. Pseudo Differential Mode with Balanced Source Impedance

Fully Differential Mode

The differential inputs of the ADA4830-1 and ADA4830-2 allow

full balanced transmission using a differential source. In this

configuration, the differential input termination is equal to twice

the source impedance of each output. For example, a source

with 37.5 Ω back termination resistors in each leg should be

terminated with a differential resistance of 75 Ω. An illustration

of this arrangement is shown in Figure 32.

INN

INP

ADA4830-1

75

Ω

−

+

37.5

Ω

37.5

Ω

POSITIVE WIRE

NEGATIVE WIRE

DRIVER PCB

DIFFERENTIAL

AMPLIFIER

Figure 32. Fully Differential Mode

VOLTAGE REFERENCE (VREF PIN)

when the differential input voltage is zero. A resistor divider

with a pair of matched 40 kΩ resistors, the divider sets this

The voltage reference pin (VREF) normally floats at its default

reference level from this default value. A voltage applied to VREF

appears at the output with unity gain, within the bandwidth limit

of the internal reference buffer. Figure 17 shows the frequency

response of the VREF input.

6 dB of attenuation (the divide-by-two provided by the reference

divider). Even when this pin is floating, it is recommended that

an external capacitor be connected from the reference node to

ground to provide further attenuation of noise on the power supply

line. A 4.7 µF capacitor combined with the internal 40 kΩ resistor

sets the low-pass corner at under 1 Hz and results in better than

40 dB of supply noise attenuation at 100 Hz.