MAX9658 Maxim, MAX9658 Datasheet - Page 10

• Manufacturer Part Number: MAX9658
• Description: The MAX9657 is a small, low-power, quad video amplifier with input sync-tip clamps
• Manufacturer: Maxim

Quad Video (Filter) Amplifiers with Input
Sync-Tip Clamps
The MAX9657 consists of input sync-tip clamps and
gain of 2V/V output amplifiers capable of driving stan-
dard 150Ω loads to ground. It can be used to buffer
video signals, for example, before a crosspoint matrix.
The MAX9658 filters and amplifies video signals. It is
very similar to the MAX9657 except that it also has inte-
grated lowpass filters. This device can be used to pro-
vide the anti-alias filtering before the video decoders of
a digital video recorder, or it can be used to do the
reconstruction filtering after a video DAC that refer-
ences output signals to the positive supply.
The MAX9657/MAX9658 feature sync-tip clamps at the
input that accept video signals with sync pulses.
Composite video with blanking and sync (CVBS) is an
example of a video signal with sync pulses. The sync-
tip voltage is internally set to 300mV.
In shutdown mode, the inputs to the MAX9657/
MAX9658 do not distort the video signal in case the
video source is driving video signals to another video
circuit such as a video multiplexer. The inputs in shut-
down mode are biased at V
above ground such that the ESD diodes never forward
bias as the video signal changes. The input resistance
is 220kΩ, which presents negligible loading on the
video current DAC.
The MAX9658 filters feature ±1dB passband out to
9.5MHz and 47dB attenuation at 27MHz, making the fil-
ter suitable for standard-definition video signals from all
sources (e.g., broadcast and DVD). Broadcast video
signals are channel limited: NTSC signals have 4.2MHz
bandwidth and PAL signals have 5MHz bandwidth.
Video signals from a DVD player, however, are not
channel limited, so the bandwidth of DVD video signals
can approach the Nyquist limit of 6.75MHz.
Recommendation: ITU-R BT.601-5 specifies 13.5MHz
as the sampling rate for standard-definition video.
Therefore, the maximum bandwidth of the signal is
6.75MHz. To ease the filtering requirements, most mod-
ern video systems oversample by two times, clocking
the video current DAC at 27MHz.
The video output amplifiers can both source and sink
load current, allowing output loads to be DC- or AC-
coupled. The amplifier output stage needs approxi-
mately 300mV of headroom from either supply rail. The
devices have an internal level-shift circuit that positions
the sync tip at approximately 300mV at the output.
10
______________________________________________________________________________________
Video Filter (MAX9658 Only)
Detailed Description
DD
/3, which is sufficiently
Outputs
Input
If the supply voltage is greater than 3.135V (5% below
a 3.3V supply), each amplifier can drive two DC-cou-
pled video loads to ground. If the supply is less than
3.135V, each amplifier can drive only one DC-coupled
or AC-coupled video load.
The devices draw approximately 35µA of supply cur-
rent when SHDN is low. In shutdown mode, the amplifi-
er outputs become high impedance.
The outputs can be AC-coupled since the output stage
can source and sink current as shown in Figure 1.
Coupling capacitors should be 220µF or greater to
keep the highpass filter, formed by the 150Ω equivalent
resistance of the video transmission line, to a corner
frequency of 4.8Hz or below. The frame rate of PAL
systems is 25Hz, the frame rate of NTSC systems is
30Hz, and the frame rate of VGA is usually 60Hz or
higher. The corner frequency should be well below the
frame rate.
The quiescent power consumption and average power
consumption of the MAX9657/MAX9658 are very low
because of the 3.3V operation and low-power circuit
design. Quiescent power consumption is defined when
the MAX9657/MAX9658 are operating without loads
and without any video signals.
Average power consumption represents the normal
power consumption when the devices drive real video
signals into real video loads. It is measured when the
MAX9657/MAX9658 drive a 150Ω load to ground with a
50% flat field, which serves as a proxy for a real video
signal.
Table 1 shows the quiescent and average power con-
sumption of the MAX9657/MAX9658.
The MAX9657/MAX9658 operate from a single-supply
voltage down to 2.7V, allowing for low-power operation.
Bypass V
external components as close as possible to the
device.
Power-Supply Bypassing and Ground
DD
to GND with a 0.1µF capacitor. Place all
Applications Information
AC-Coupling the Outputs
Power Consumption
Shutdown