Data Sheet
Comlinear CLC2000, CLC4000 High Output Current Dual and Quad Ampliers Rev 1D
©2007-2013 Exar Corporation 15/18 Rev 1D
Overdrive Recovery
An overdrive condition is dened as the point when ei-
ther one of the inputs or the output exceed their specied
voltage range. Overdrive recovery is the time needed for
the amplier to return to its normal or linear operating
point. The recovery time varies, based on whether the in-
put or output is overdriven and by how much the range is
exceeded. The CLC2000/CLC4000 will typically recover in
less than 40ns from an overdrive condition. Figure 5 shows
the CLC2000 in an overdriven condition.
Figure 5. Overdrive Recovery
Using the CLC2000/CLC4000 as a Differential Line Driver
The combination of good large signal bandwidth and high
output drive capability makes the CLC2000/CLC4000 well
suited for low impedance line driver applications, such
as the upstream data path for a ADSL CPE modem. The
dual channel conguration of the CLC2000 provides bet-
ter channel matching than a typical single channel device,
resulting in better overall performance in differential ap-
plications. When congured as a differential amplier as
in gure 6, it can easily deliver the 13dBm to a standard
100Ω twisted-pair CAT3 or CAT5 cable telephone network,
as required in a ADSL CPE application.
Differential circuits have several advantages over single-
ended congurations. These include better rejection of
common mode signals and improvement of power-supply
rejection. The use of differential signaling also improves
overall dynamic performance. Total harmonic distortion
(THD) is reduced by the suppression of even signal har-
monics and the larger signal swings allow for an improved
signal to noise ratio (SNR).
+
VIN
Vo+
1:2
Vo-
Ro+=12.5Ω
RL=100Ω
Ro-=12.5Ω
1/2
CLC2000
1/2
CLC2000
Rg
Rf+
-
Rf-
VOUT
-Vs
+Vs
Figure 6: Typical Differential Transmission Line Driver
For any transmission requirement, the fundamental de-
sign parameters needed are the effective impedance of
the transmission line, the power required at the load, and
knowledge concerning the content of the transmitted sig-
nal. The basic design of such a circuit is briey outlined
below, using the ADSL parameters as a guideline.
Data transmission techniques, such as ADSL, utilize ampli-
tude modulation techniques which are sensitive to output
clipping. A signal’s PEAK to RMS ratio, or Crest Factor (CF),
can be used to determine the adequate peak signal levels
to insure delity for a given signal.
For an ADSL system, the signal consists of 256 indepen-
dent frequencies with varying amplitudes. This results in
a noise-like signal with a crest factor of about 5.3. If the
driver does not have enough swing to handle the signal
peaks, clipping will occur and amplitude modulated infor-
mation can be corrupted, causing degradation in the sig-
nals Bit Error Rate.
To determine the required swing, rst use the specied
load impedance to convert the RMS power to an RMS volt-
age. Then, multiply the RMS voltage by the crest factor to
get the peak values. For example 13dBm, as referenced to
1mW, is ~20mW. 20mW into the 100Ω CAT5 impedance
yields a RMS voltage of 1.413 VRMS . Using the ADSL crest
factor of 5.3 yields ~ ±7.5V peak signals.
-6
-4
-2
0
2
4
6
-3
-2
-1
0
1
2
3
020 40 60 80 100 120 140 160 180 200
Output
Input
V
IN
= 2.5V
pp
G = 5