LT6210_15 Datasheet, PDF (14/18 Pages) Linear Technology – Single/Dual Programmable Supply Current, R-R Output, Current Feedback Amplifiers

LT6210/LT6211
Typical Applications
3V Cable Driver with Active Termination
Driving back-terminated cables on single supplies usually
results in very limited signal amplitude at the receiving
end of the cable. However, positive feedback can be used
to reduce the size of the series back termination resistor,
thereby decreasing the attenuation between the series
and shunt termination resistors while still maintaining
controlled output impedance from the line-driving amplifier.
Figure 3 shows the LT6210 using this “active termination”
scheme on a single 3V supply. The amplifier is AC-coupled
and in an inverting gain configuration to maximize the input
signal range. The gain from V_IN to the receiving end of the
cable, V_OUT, is set to –1. The effective impedance looking
into the amplifier circuit from the cable is 50Ω throughout
the usable bandwidth.
The response of the cable driver with a 1MHz sinusoid is
shown in Figure 4. The circuit is capable of transmitting
a 1.5V_P-P undistorted sinusoid to the 50Ω termination
resistor and has a full signal 1V_P-P bandwidth of 50MHz.
Small signal –3dB bandwidth extends from 1kHz to 56MHz
with the selected coupling capacitors.
3V
2k ^2k
1.3k
1% ^1%
1%
2.2µF
249Ω
1%
V_IN
3V
4₊
6
LT6210
3_–
R_SER
15Ω
1 ^1%
2 VA
5
154Ω
1%
2.2µF
3300pF
NPO
V_OUT
R_TERM
50Ω
6210 F03
Figure 3. 3V Cable Driver with Active Termination
V_IN
1V/DIV
V_A
1V/DIV
V_OUT
1V/DIV
200ns/DIV
6210 F04
Figure 4. Response of Circuit at 1MHz
Simplified Schematic
V⁺
6
+IN
3
600Ω
600Ω
8k SUPPLY
CURRENT
CONTROL
V^–
5
I_SET
2
V⁺
–IN
OUT
4
OUTPUT BIAS
1
CONTROL
V^–
6210 SS
62101fc
14