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參數資料
| 型號： | GT4123A |
| 廠商： | Gennum Corporation |
| 英文描述： | Two Channel Video Multipliers |
| 中文描述： | 雙通道視頻乘法器 |
| 文件頁數： | 4/7頁 |
| 文件大?。?/td> | 157K |
| 代理商： | GT4123A |
4
520 - 38 - 3
DETAILED DESCRIPTION
The GT4123 and GT4123A are the first dedicated single
device, two input video mixer ICs available to the professional
video and multimedia markets.
The internal topology of the devices is shown in Figure 1.
Fig. 1 Functional Block Diagram of the GT4123 and GT4123A
Each input signal is applied to a conventional differential
amplifier (AMP A and AMP B). From the amplifiers, the signals
are applied to analog multiplier circuits (XA and XB) whose
outputs are the product of the input signals and internally
generated controlling voltages V
CA
and V
CB
.
These voltages are derived from a unity gain differential
amplifier (AMP C) whose outputs (true and invert) are the
difference between an externally applied CONTROL voltage
(V
) and an internal 0.5 volt reference voltage. In addition, the
internal DC offset of 0.5 volts is applied to the controlling
voltage summing circuits
Σ
2 and
Σ
3.
Therefore,
V
CA
= 0.5V + (VC - 0.5V) and
V
CB
= 0.5V - (VC - 0.5V)
When the CONTROL input (V
) equals 0.5 volts, V
and
V
= 0.5 volts and exactly 50% of each input signal passes
to the output of the multiplier stages.
When V
is less than 0.5 volts, V
reduces and V
increases
in proportion so that less of the Channel A signal and more of
the Channel B signal is transferred. Similarly, when V
C
is
greater than 0.5 volts, the opposite occurs.
The SPAN or control range is internally set so that a CONTROL
voltage of 0 volts completely cuts off Channel A and fully turns
on Channel B. Similarly, a CONTROL voltage of 1 volt will fully
turn on Channel A and completely turn Channel B off.
Figure 10 shows the CONTROL transfer characteristics of the
GT4123 and GT4123A.
There is a small ‘dead band’ at either extreme of the CONTROL
input. The amount of ‘dead band’ is about 100 mV and is
shown in Figure 10. The CONTROL input can be preceded by
an operational amplifier so biased as to overcome this ‘dead
band’ as well as level shift the control signal so that other than
0 to 1 volt ranges can be used. The bandwidth of the
CONTROL input is sufficient to allow very fast keying and is in
the order of 20 MHz at -0.1 dB.
The linear portion of the transfer characteristic has a linearity
of 1% or better.
The outputs from the multipliers are applied to an analog
summing circuit (
Σ
1) whose output feeds a wideband amplifier
(Amp D) and presents the mixed signals to the outside world.
The inverting inputs of each input amplifier are directly
connected to the output.
In this manner the closed loop gain is nearly unity providing
wideband, stable operation. Because the devices have only
8 pins and require virtually no external parts in order to
function, they lend themselves to high density, multi-functional
PC board layouts. Several devices can be used in parallel
applications such as R-G-B mixers and four-layer keyers
where close control law tracking is essential.
The only difference between the GT4123 and the GT4123A is
the fact that the latter device can operate with non-equal
power supplies. The negative supply can be as low as -3 volts
unlike the GT4123 which can only operate down to
±
9 volt
supplies.
COMP
V
CA
= 0.5 + (V
C
- 0.5)
+
V
CB
OUT
+
IN A
IN B
CO)
(V
C
+
+
+
V
CB
= 0.5 - (V
C
- 0.5)
+
+
-
AMP D
AMP C
-
XB
XA
-
+
AMP A
0.5V
REF
V
CA
Σ1
Σ2
Σ3
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相關代理商/技術參數 |
參數描述 |
|---|---|
| GT4123ACDA | 制造商:Rochester Electronics LLC 功能描述: 制造商:Gennum Corporation 功能描述: |
| GT4123ACKA | 制造商:Rochester Electronics LLC 功能描述: 制造商:Gennum Corporation 功能描述: |
| GT4123ACKAE3 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Gennum Corporation 功能描述: |
| GT4123B | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Two Channel Video Multiplier |
| GT4123BCDA | 制造商:Rochester Electronics LLC 功能描述: 制造商:Gennum Corporation 功能描述: |
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