ISL59601 Datasheet, PDF (21/27 Pages) Intersil Corporation – MegaQ: An Automatic Composite Video Equalizer, Fully-Adaptive to 1 Mile (1600m)

ISL59601, ISL59602, ISL59603, ISL59604, ISL59605
Application Information
UTP Application Circuit
Figure 45 shows the complete schematic for a MegaQ™
equalizer configured for UTP cable. The input signal is
terminated into the network formed by R1, R2, and R3.
The original datasheet and evaluation boards
recommended different values for the termination
network as well as an additional resistor and capacitor
that were not necessary. C1 and C2 AC-couple the signal
into MegaQ™.
On the output side, C5, R5, and C4 form a compensation
network, while R6 provides 75Ω source-termination for
the video output. MegaQ™ has an native gain of 6dB, so
when VIDEO OUT is terminated into 75Ω (the input to a
DVR, TV, etc.), R6 and the 75Ω terminator form a 2:1
divider, producing standard video amplitude across the
75Ω terminator.
Coax Input Circuit
Figure 46 shows the input termination recommended for
coaxial cables, which is the same as that used for UTP
cables except for the addition of C10, which bypasses
high-frequency noise on the coax ground line to system
ground. This allows the coax ground to be independent of
the system at low frequencies (DC to 50/60Hz) to
accommodate differences in the ground potential of the
remote video source(s). The original datasheet and
evaluation boards had a more complex network that did
not perform as well as this one, but they can be easily
modified (with component substitutions only) to match
this one.
COAX
C10
0.1μF
R3 ^R1
1k
R2
C1
1.0μF ^IN+
37.4
37.4
MegaQ™
IN-
C2 ^1.0μF
FIGURE 46. APPLICATION CIRCUIT FOR COAX CABLE
Dual UTP/Coax Input Circuit
If desired, it is also possible to support both UTP and
coax cables with the same PCB layout. Since the
termination network is very similar for both UTP and
coax, this becomes as simple as having both connectors
tied to the input network, adding a switch to introduce
C10 when in coax mode, and making a minor
compromise on the termination values when using UTP.
Note that only coax or UTP should be connected at any
one time - this circuit does not multiplex between them.
Terminating UTP into 75Ω instead of 100Ω results in no
detectable change in the quality of the output signal,
while terminating 75Ω coax into 100Ω does significantly
degrade the video. Terminating UTP into 75Ω will slightly
attenuate the input signal, however MegaQ™’s AGC
capability compensates for the loss.
21
Input Multiplexing
Placing a semiconductor multiplexer in front of this part
may increase high frequency attenuation and noise.
However a low-capacitance mechanical relay may be
acceptable. Note that changing from one channel to
another in Lock Until Reset mode will require a reset
(INVERT toggle) to trigger equalization of the new
channel (see “Lock Until RESET” on page 21).
UTP
IN+
COAX
UTP
IN-
R3 ^R1
1k
R2
SW1
(Close for
C10 ^COAX)
C1
1.0μF
37.4
37.4
1.0μF
C2
IN+
IN-
0.1μF
MegaQ™
FIGURE 47. APPLICATION CIRCUIT FOR COAX CABLE
For best performance, do not multiplex the inputs to the
equalizer - this can further degrade the signal. Instead,
multiplex at the output after equalization has been
performed.
Stand-Alone Operation and Configuration
In its default stand-alone configuration, MegaQ™
features two modes of automatic cable equalization:
Lock Until Reset and Continuous Update. Lock Until
Reset is the recommended mode for most applications.
LOCK UNTIL RESET
In the Lock Until Reset mode, once MegaQ™ finds the
optimum equalization and the LOCKED signal goes high,
the equalization is frozen and will not change until either
the power is cycled or the INVERT signal is toggled,
which initiates a re-equalization of the input signal. Re-
equalization is usually only necessary during
device/system evaluation - in normal operation MegaQ™
powers-up, acquires and equalizes the signal, and
continues to equalize until/unless it is powered-down. If
the signal is lost in Lock Until Reset mode, the LOCKED
pin will not go low until/unless the device is reset by
toggling the INVERT pin. A reset should only be
necessary if the length or type of cable was changed
without cycling power.
To enable the Lock Until Reset mode, tie the LOCKED
output pin to the FREEZE input pin as shown in Figure 45
on page 20.
To generate a reset (and trigger a re-equalization),
toggle the external INVERT pin. Depending on the initial
state of INVERT, this would be a high-low-high or
low-high-low sequence.
CONTINUOUS UPDATE
In the Continuous Update mode, MegaQ™ will
continuously try to find the optimum equalization
solution. When the equalization has settled for 100
sequential video lines with no changes, the LOCKED pin
FN6739.1
November 23, 2010