Texas Instruments THS7373EVM Evaluation Module THS7373EVM THS7373EVM 데이터 시트
제품 코드
THS7373EVM
SBOS506A – DECEMBER 2009 – REVISED AUGUST 2012
Keep in mind that the internal 800-k
Ω
resistor has
Additionally, the time to charge the capacitor to the
approximately
a
±20%
variance.
As
such,
the
final dc bias point is a function of the pull-up resistor
calculations should take this variance into account.
and the input capacitor. Lastly, the input capacitor
For the 0.644-V example above, using an ideal 3.3-
forms a high-pass filter with the parallel impedance of
M
Ω
resistor,
the
input
dc
bias
voltage
is
the pull-up resistor and the 800-k
Ω
resistor. In
approximately 0.644 V ± 0.1 V.
general, it is good to have this high-pass filter at
approximately 3 Hz to minimize any potential droop
approximately 3 Hz to minimize any potential droop
The value of the output bias voltage is very flexible
on a P’
B
or P’
R
signal. A 0.1-
μ
F input capacitor with a
and is left to each individual design. It is important to
3.3-M
Ω
pull-up resistor equates to approximately a
ensure that the signal does not clip or saturate the
2.5-Hz high-pass corner frequency.
video signal. Thus, it is recommended to ensure the
output bias voltage is between 0.9 V and (V
output bias voltage is between 0.9 V and (V
S+
– 1 V).
AC biasing is recommended for use with component
For 100% color saturated CVBS or signals with
video P’
B
, P’
R
, U’, or V’ signals because these signals
Macrovision
®
, the CVBS signal can reach up to
either have no embedded sync or the sync is a mid-
1.23 V
PP
at the input, or 2.46 V
PP
at the output of the
level sync rather than a bottom-level sync. This
THS7373. In contrast, other signals are typically
method can also be used with sync signals if desired.
1 V
PP
or 0.7 V
PP
at the input which translate to an
The benefit of using the STC function is that it
output voltage of 2 V
PP
or 1.4 V
PP
. The output bias
maintains a constant back-porch voltage as opposed
voltage must account for a worst-case situation,
to a back-porch voltage that fluctuates depending on
depending on the signals involved.
the
video
content.
Because
the
input
corner
frequency is a very low 2.5 Hz, the input corner
One other issue that must be taken into account is
frequency is also a very low 2.5 Hz, which is
the dc-bias point is a function of the power supply. As
respectable (relative to a STC configuration).
such, there is an impact on system power-supply
rejection ratio (PSRR). To help reduce this impact,
the
rejection ratio (PSRR). To help reduce this impact,
the
input
capacitor
combines
with
the
pull-up
resistance
to
function
as
a
low-pass
filter.
Copyright © 2009–2012, Texas Instruments Incorporated
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