VCA2619 Datasheet, PDF (9/16 Pages) Burr-Brown (TI) – Dual, Variable Gain Amplifier with Input Buffer

VCA2619
www.ti.com
SBOS276A − AUGUST 2003 − REVISED AUGUST 2003
TYPICAL CHARACTERISTICS (continued)
At TA = 25°C and VDD = 5V, load resistance = 500Ω on each output to ground, differential output (2VPP) MGS = 111, and fIN = 5MHz, unless
otherwise noted.
0
−10
−20
−30
−40
−50
−60
1M
OVERLOAD DISTORTION vs FREQUENCY
0.2V
0.3V
0.5V
1V
10M
Frequency (Hz)
I_CC (CHA and CHB) vs TEMPERATURE
55
54
53
52
51
50
49
48
47
46
45
−40 −30 −20 −10 0 10 20 30 40 50 60 70 80 90
Temperature (_C)
OVERVIEW
The VCA2619 is a dual-channel, VGA consisting of three
primary blocks: an Input Buffer, a VCA, and a PGA. All
stages are ac coupled, with the coupling into the PGA
stage being made variable by placing an external capaci-
tor between the CP1 and CP2 pins. This will be discussed
further in the PGA section. By using the internal coupling
into the PGA, the result is a high-pass filter characteristic
with cutoff at approximately 75kHz. The output PGA natu-
rally rolls off at around 30MHz, making the usable band-
width of the VCA2619 between 75kHz and 30MHz.
Channel A
Input
Buffer
VCA
PGA
Channel A
Output
INPUT BUFFER
The input buffer is a unity gain amplifier (gain of +1) with
a bandwidth of 100MHz with an input resistance of approx-
imately 600kΩ. The input buffer isolates the circuit driving
the VCA2619 inputs from the internal VCA block, which
would present a varying impedance to the input circuitry.
To allow symmetrical operation of the input buffer, the input
to the buffer must be ac coupled through an external ca-
pacitor. The recommended value of the capacitor is
0.01µF. It should be noted that if the capacitor value were
increased, the power-on time of the VCA2619 would be in-
creased. If a decrease in the power-on time is needed, the
value can be decreased to no less than 100pF.
VCA
Control
Analog
Control
Maximum
Gain
Select
MGS
Channel B
Input
Buffer
VCA
PGA
Channel B
Output
Figure 1. Simplified Block Diagram of the
VCA2619.
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