ada4830-1 Analog Devices, Inc., ada4830-1 Datasheet - Page 11

• Manufacturer Part Number: ada4830-1
• Description: High Speed Difference Amplifier With Input Short To Battery Protection
• Manufacturer: Analog Devices, Inc.

Data Sheet
APPLICATIONS INFORMATION
METHODS OF TRANSMISSION
Pseudo Differential Mode (Unbalanced Source
Termination)
The
configuration with an unbalanced input signal. This allows
the receiver to be driven by any 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.
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 21.
Pseudo Differential Mode (Balanced Source Impedance)
Pseudo differential signaling is typically implemented using
unbalanced source termination as shown in Figure 21. 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 22. Splitting
the source termination resistance evenly between the hot and
cold conductors results in matched attenuation of the common-
mode signals, ensuring maximum rejection.
Figure 22. Pseudo Differential Mode with Balanced Source Impedance
ADA4830-1
SINGLE ENDED
SINGLE ENDED
AMPLIFIER
AMPLIFIER
DRIVER PCB
DRIVER PCB
Figure 21. Pseudo Differential Mode
can be operated in a pseudo differential
37.5Ω
37.5Ω
75Ω
NEGATIVE WIRE
NEGATIVE WIRE
POSITIVE WIRE
POSITIVE WIRE
+
−
+
−
75Ω
75Ω
INN
INN
INP
INP
ADA4830-1
ADA4830-1
Rev. 0 | Page 11 of 16
Fully Differential Mode
The differential inputs of the
transmission using any 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 23.
VOLTAGE REFERENCE (VREF PIN)
An internal reference level determines the output voltage when
the differential input voltage is zero. This is set by a resistor
divider connected between the supply rails. Built with a matched
pair of 40 kΩ resistors, the divider sets this voltage to +V
The voltage reference pin (VREF) normally floats at its default
value of +V
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.
Any noise on the +V
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.
INPUT COMMON-MODE RANGE
In a standard four resistor difference amplifier with 0.5 V/V
gain, the input common-mode (CM) range is three times the
CM range of the core amplifier. In the ADA4830-1, however,
the input CM has been extended to more than 17 V (with a 5 V
supply). The input CM range can be approximated by using the
following formulas:
Maximum CM voltage
Minimum CM voltage
5(+V
−10 V ≤ V
DIFFERENTIAL
AMPLIFIER
S
− 1.25) − 4V
S
/2. However, it can be used to vary the output
DRIVER PCB
INCM(MIN)
Figure 23. Fully Differential Mode
S
37.5Ω
37.5Ω
supply rail appears at the output with only
≈ − (1 + 4V
REF
≈ V
NEGATIVE WIRE
POSITIVE WIRE
ADA4830-1
INCM(MAX)
+
−
REF
)
≤ 9.5 V
75Ω
INP
INN
allow full balanced
ADA4830-1
ADA4830-1
S
/2.