Data Sheet
which offsets the current output. If BLANK = Low, data
inputs and the pedestal are disabled.
Functional Description
Within the CDK3400/3401 are three identical 10-bit D/A
converters, each with a current source output. External
loads are required to convert the current to voltage out-
puts. Data inputs RGB7-0 are overridden by the BLANK
input. SYNC = H activates, sync current from I for sync-
on-green video signals.
Sync Pulse Input - SYNC
Bringing SYNC LOW, turns off a 40 I (7.62mA) current
RE
source which forms a sync pulse on the Green D/A con-
verter output. SYNC is registered on the rising edge of
CLK with the same pipeline latency as BLANK and pixel
data. SYNC does not override any other data and should
be used only during the blanking interval.
OS
Digital Inputs
All digital inputs are TTL-compatible. Data is registered
on the rising edge of the CLK signal. Following one stage
Since this is a single-supply D/A and all signals are posi-
tive-going, sync is added to the bottom of the Green D/A
range. So turning SYNC OFF means turning the current
source ON. When a sync pulse is desired, the current
source is turned OFF. If the system does not require sync
pulses from the Green D/A converter, SYNC should con-
nected to GND.
of pipeline delay, the analog output changes t after the
DO
rising edge of CLK.
Clock Input - CLK
The clock input is TTL-compatible and all pixel data is
registered on the rising edge of CLK. It is recommended
that CLK be driven by a dedicated TTL buffer to avoid
reflection induced jitter, overshoot, and undershoot.
Blanking Input - BLANK
When BLANK is LOW, pixel inputs are ignored and the
D/A converter outputs fall to the blanking level. BLANK
is registered on the rising edge of CLK and has the same
pipeline latency as SYNC.
Pixel Data Inputs - R9-0, B9-0, G9-0
TTL-compatible Red, Green and Blue Data Inputs are reg-
istered on the rising edge of CLK.
D/A Outputs
Each D/A output is a current source. To obtain a voltage
output, a resistor must be connected to ground. Output
voltage depends upon this external resistor, the reference
voltage, and the value of the gain-setting resistor con-
SYNC and BLANK
SYNC and BLANK inputs control the output level (Figure 2
and Table 1, on the previous page) of the D/A converters
during CRT retrace intervals. BLANK forces the D/A outputs
to the blanking level while SYNC = L turns off a current
source that is connected to the green D/A converter. SYNC
nected between R
and GND.
REF
Normally, a source termination resistor of 75Ω is connect-
ed between the D/A current output pin and GND near the
D/A converter. A 75Ω line may then be connected with an-
other 75Ω termination resistor at the far end of the cable.
This “double termination” presents the D/A converter with
a net resistive load of 37.5Ω.
= H adds a 40 I sync pulse to the green output, SYNC =
RE
L sets the green output to 0.0V during the sync tip. SYNC
and BLANK are registered on the rising edge of CLK.
The CDK3400/3401 may also be operated with a single
75Ω terminating resistor. To lower the output voltage
swing to the desired range, the nominal value of the
Data: 660mV max.
resistor on R
should be doubled.
REF
Pedestal: 54mV
Sync: 286mV
R, G, and B Current Outputs - IO , IO , IO
B
R
G
The R, G, and B current source outputs of the D/A
converters are capable of driving RS-343A/SMPTE-170M
compatible levels into doubly-terminated 75Ω lines. Sync
pulses may be added to the Green D/A output.
Figure 2. Normal Output Levels
BLANK gates the D/A inputs and sets the pedestal voltage.
If BLANK = HIGH, the D/A inputs are added to a pedestal
©2008 CADEKA Microcircuits LLC
www.cadeka.com
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