ISL15100

6

FN8577.0

September 19, 2013

Applications Information

Product Description

The ISL15100 is a differential operational amplifier designed for

line driving in power line communications (PLC). It is a low

distortion, current mode feedback amplifier that draws

moderately low supply current. Due to the current feedback

architecture, the ISL15100 closed-loop -3dB bandwidth is

dependent on the value of the feedback resistor. The desired

Feedback Resistor Values

wider bandwidth at the expense of slight peaking, can be

obtained by reducing the value of the feedback resistor.

Inversely, larger values of the feedback resistor will cause rolloff

to occur at a lower frequency.

Quiescent Current vs Temperature

The ISL15100 was designed to have the quiescent current

increase with temperature, which maintains good distortion

performance at high temperatures.

Supply Voltage Range

The ISL15100 operates with bipolar supply voltages from ±4.0V

to ±6.6V (±6.65V maximum). Optimum bandwidth, slew rate,

and video characteristics are obtained at higher supply voltages.

Single Supply Operation

If a single supply is desired, values from +8.0V to +13.2V (+13.3V

maximum) can be used as long as the input common mode

range is not exceeded. When using a single supply, be sure to

either:

1. DC bias the inputs at an appropriate common mode voltage

and AC-couple the signal.

2. Ensure the driving signal is within the common mode range of

the ISL15100.

Multi-Tone Power Ratio (MTPR)

G.hn PLC uses OFDM modulation to digitally encode data for

communication. A carrier spacing of 24.41kHz is used in power

lines, and 48.82kHz is used in phone lines.

In multi-tone signaling, linearity is shown in the MTPR

measurement. MTPR measures the difference in power of a

carrier tone vs. a missing tone.

Figure 4 shows ISL15100's MTPR performance for a narrow

frequency span.

Disable Linearity

Unlike DSL, communication in PLC systems is half duplex

meaning only one device can transmit at a time. When the line

driver is not transmitting, it is disabled and the receiver is

enabled. Figure 5 shows the shared transmit and receive signal

path of two ends. When Txa is transmitting, optimal MTPR is

achieved if Txb is removed. Since Txb cannot be removed, the

best MTPR occurs if the line driver is a very high impedance

when disabled.

impedance to the transformer, thus setting its frequency span.

-100

-90

-80

-70

-60

-50

-40

-30

1.50

1.52

1.54

1.56

1.58

1.60

FREQUENCY (MHz)

MTPR

FIGURE 4. PLC SIGNAL TONES WITH 25kHz SPACING

FIGURE 5. Tx AND Rx SIGNAL PATH. CASE1:[Txa: ON, Rxa: OFF, Txb: OFF, Rxb: ON]. CASE2:[Txa: OFF, Rxa: ON, Txb: ON, Rxb: OFF]