Datasheet

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WIDEBAND, INVERTING OPERATION
_
+
R
G
402 Ω
0.1 µF 6.8 µF
−V
S
−15 V
50 Ω Source
+
V
I
0.1 µF 6.8 µF
+
+V
S
15 V
R
F
806 Ω
R
M
57.6 Ω
49.9 Ω
50 Ω LOAD
_
+
49.9 Ω
50 Ω Source
V
I
+V
S
R
F
909 Ω
R
G
909 Ω
+V
S
2
+V
S
2
_
+
402 Ω
50 Ω Source
V
I
V
S
R
F
806 Ω
+V
S
2
+V
S
2
57.6 Ω
R
G
R
T
R
T
49.9 Ω
49.9 Ω
50 Ω LOAD
50 Ω LOAD
SINGLE SUPPLY OPERATION
VDSL Driver Circuit
THS3092
THS3096
SLOS428B – DECEMBER 2003 – REVISED FEBRUARY 2006
Figure 53 shows the THS3092 in a typical inverting
gain configuration where the input and output
impedances and signal gain from Figure 52 are
retained in an inverting circuit configuration.
Figure 53. Wideband, Inverting Gain
Configuration
Figure 54. DC-Coupled, Single-Supply Operation
The THS3092/6 have the capability to operate from a
The THS3092 and THS3096 have the ability to drive
single supply voltage ranging from
over 200 mA of current with very high voltage swings.
10 V to 30 V. When operating from a single power
Using these amplifiers coupled with the very high
supply, biasing the input and output at mid-supply
slew rate, low distortion, and low noise required in
allows for the maximum output voltage swing. The
VDSL applications, makes for a perfect match. In
circuits shown in Figure 54 shows inverting and
VDSL systems where the receive signal is critical, the
noninverting amplifiers configured for single supply
use of a low transformer ratio is necessary. With this
operations.
low ratio, the output swing required from the line
driver amplifier must increase, especially when
driving the VDSL’s full 14.5-dBm power onto the line.
The line driver's low distortion and noise is critical for
the VDSL as the receive bands are intertwined with
the transmit frequency bands up to the 12-MHz VDSL
limit.
Figure 55 shows a traditional hybrid connection
approach for achieving the 14.5-dBm line power
utilizing a 1:1 transformer. Looking at the input to the
amplifiers shows a low-pass filter consisting of two
separate capacitors to ground. There is an argument
that since the signal coming out of the DAC is
fully-differential then a single capacitor (10 pF in this
case) is perfectly acceptable. The problem with this
idea is that many DACs have common-mode energy
due to images around the sampling frequency which
must be filtered before reaching the amplifier. An
amplifier simply amplifies its input–including the
DAC’s images at high frequencies–and pass it
through to the transformer and ultimately to the line,
possibly causing the system to fail EMC compliance.
A single capacitor does not remove these
17
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