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PDF VCA810 Data sheet ( Hoja de datos )
| Número de pieza | VCA810 | |
| Descripción | High Gain Adjust Range/ Wideband/ Voltage-Controlled Amplifier | |
| Fabricantes | Burr-Brown Corporation | |
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VCA810
SBOS275C − JUNE 2003 − REVISED OCTOBER 2004
High Gain Adjust Range, Wideband,
Voltage-Controlled Amplifier
FEATURES
D HIGH GAIN ADJUST RANGE: +40dB
D DIFFERENTIAL IN/SINGLE-ENDED OUT
D LOW INPUT NOISE VOLTAGE: 2.4nV//Hz
D CONSTANT BANDWIDTH vs GAIN: 35MHz
D HIGH dB/V GAIN LINEARITY: +0.3dB
D GAIN CONTROL BANDWIDTH: 25MHz
D LOW OUTPUT DC ERROR: < +40mV
D HIGH OUTPUT CURRENT: +60mA
D LOW SUPPLY CURRENT: 24.8mA (max for
−405C to +855C temperature range)
APPLICATIONS
D OPTICAL RECEIVER TIME GAIN CONTROL
D SONAR SYSTEMS
D VOLTAGE-TUNABLE ACTIVE FILTERS
D LOG AMPLIFIER
D PULSE AMPLITUDE COMPENSATION
D AGC RECEIVER WITH RSSI
D IMPROVED REPLACEMENT FOR THE
VCA610
1
V+
8
V−
2
+5V
6
VCA810
G a in
Adjust
+
X1 5 VOUT
VC
0 → −2V
− 40dB → +40dB Gain
3
7
−5V
DESCRIPTION
The VCA810 is a DC-coupled, wideband, continuously
variable, voltage-controlled gain amplifier. It provides a
differential input to single-ended output conversion with a
high-impedance gain control input used to vary the gain over
a –40dB to +40dB range linear in dB/V.
Operating from ±5V supplies, the gain control voltage for the
VCA810 will adjust the gain from –40dB at 0V input to +40dB
at –2V input. Increasing the control voltage above ground will
attenuate the signal path to > 80dB. Signal bandwidth and
slew rate remain constant over the entire gain adjust range.
This 40dB/V gain control is accurate within ±1.5dB (±0.9dB
for High Grade), allowing the gain control voltage in an AGC
application to be used as a Received Signal Strength
Indicator (RSSI) with ±1.5dB accuracy.
Excellent common-mode rejection and common-mode input
range at the two high-impedance inputs allow the VCA810 to
provide a differential receiver operation with gain adjust. The
output signal is referenced to ground. Zero differential input
voltage gives a 0V output with a small DC offset error. Low
input noise voltage ensures good output SNR at the highest
gain settings.
In applications where pulse edge information is critical, and
the VCA810 is being used to equalize varying channel loss,
minimal change in group delay over gain setting will retain
excellent pulse edge information.
An improved output stage provides adequate output current
to drive the most demanding loads. While principally intended
to drive analog-to-digital converters (ADCs) or 2nd-stage
amplifiers, the ±60mA output current will easily drive
doubly-terminated 50Ω lines or a passive post filter stage
over the ±1.7V output voltage range.
VCA810 RELATED PRODUCTS
SINGLES DUALS
GAIN ADJUST
RANGE (dB)
INPUT
NOISE
(nV//Hz)
VCA811
—
80
2.4
— VCA2612
45
1.25
— VCA2613
45
1
— VCA2614
45
3.6
— VCA2616
45
3.3
— VCA2618
45
5.5
SIGNAL
BANDWIDTH
(MHz)
80
80
80
40
40
30
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments
semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date. Products
conform to specifications per the terms of Texas Instruments standard warranty.
Production processing does not necessarily include testing of all parameters.
Copyright 2003−2004, Texas Instruments Incorporated
www.ti.com
1 page  
VCA810
www.ti.com
SBOS275C − JUNE 2003 − REVISED OCTOBER 2004
HIGH GRADE DC SPECIFICATIONS: VS = +5V (VCA810AID) (continued)
Boldface limits are tested at +255C.
RL = 500Ω, and VIN = single-ended input on V+ with V− at ground, unless otherwise noted.
VCA810AID
TYP MIN/MAX OVER TEMPERATURE
PARAMETER
CONDITIONS
+0°C to −40°C to
MIN/
TEST
+25°C +25°C(1) +70°C(2) +85°C(2) UNITS MAX LEVELS(3)
POWER SUPPLY
Positive Supply Quiescent Current
Maximum Quiescent Current
Minimum Quiescent Current
Maximum Quiescent Current
Minimum Quiescent Current
Negative Supply Quiescent Current(5)
+VS = +5V, G = −40dB
+VS = +5V, G = −40dB
+VS = +5V, G = +40dB
+VS = +5V, G = +40dB
10 11.5 11.6 11.7 mA min
10 8.5 8.2 8.1 mA max
18 19.5
21
21.3
mA min
18
16.5
15.5
14.5
mA max
A
A
A
A
Maximum Quiescent Current
−VS = −5V, G = −40dB
12
14
14.1
14.2
mA min
A
Minimum Quiescent Current
−VS = −5V, G = −40dB
12 10
9.9 9.8 mA max
A
Maximum Quiescent Current
−VS = −5V, G = +40dB
20 22
24
24.3
mA min
A
Minimum Quiescent Current
−VS = −5V, G = +40dB
20 18
17
16.5
mA max
A
(1) Junction temperature = ambient for +25°C specifications.
(2) Junction temperature = ambient at low temperature limit; junction temperature = ambient +30°C at high temperature limit for over temperature specifications.
(3) Test levels: (A) 100% tested at +25°C. Over temperature limits by characterization and simulation. (B) Limits set by characterization and simulation.
(C) Typical value only for information.
(4) Maximum deviation from best line fit.
(5) Magnitude.
5
5 Page 
VCA810
www.ti.com
APPLICATIONS INFORMATION
CIRCUIT DESCRIPTION
The VCA810 is a high gain adjust range, wideband,
voltage amplifier with a voltage-controlled gain, as shown
in Figure 1. The circuit’s basic voltage amplifier responds
to the control of an internal gain-control amplifier. At its
input, the voltage amplifier presents the high impedance of
a differential stage, permitting flexible input impedance
matching. To preserve termination options, no internal
circuitry connects to the input bases of this differential
stage. For this reason, the user must provide DC paths for
the input base currents from a signal source, either through
a grounded termination resistor or by a direct connection
to ground. The differential input stage also permits
rejection of common-mode signals. At its output, the
voltage amplifier presents a low impedance, simplifying
impedance matching. An open-loop design produces wide
bandwidth at all gain settings. A ground-referenced
differential to single-ended conversion at the output retains
the low output offset voltage.
+5V
1
V+
8
V−
2
3
VC
0 → −2V
−40dB → +40dB Gain
VCA810
Gain
Adjust
+
X1
VOUT
−5V
Figure 1. Block Diagram of the VCA810
A gain control voltage, VC, controls the amplifier gain
magnitude through a high-speed control circuit. Gain
polarity can be either inverting or non-inverting, depending
upon the amplifier input driven by the input signal. The gain
control circuit presents the high-input impedance of a
non-inverting op amp connection. The control voltage pin
is referred to ground as shown in Figure 1. The control
voltage VC varies the amplifier gain according to the
exponential relationship GǒVńVǓ + 10*2(VC)1).
This translates to the log gain relationship
G(dB) + *40 @ ǒVC)1Ǔ dB. Thus, G(dB) varies linearly
over the specified −40dB to +40dB range as VC varies from
SBOS275C − JUNE 2003 − REVISED OCTOBER 2004
0V to −2V. Optionally, making VC slightly positive (≥
+0.15V) effectively disables the amplifier, giving > 80dB of
signal path attenuation at low frequencies.
Internally, the gain-control circuit varies the amplifier gain
by varying the transconductance, gm, of a bipolar
transistor using the transistor bias current. Varying the bias
currents of differential stages varies gm to control the
voltage gain of the VCA810. A gm-based gain adjust
normally suffers poor thermal stability. The VCA810
includes circuitry to minimize this effect.
VCA810 OPERATION
Figure 2 shows the circuit configuration used as the basis
of the Electrical Characteristics and Typical
Characteristics. Voltage swings reported in the
specifications are taken directly at the input and output
pins. For test purposes, the input impedance is set to 50Ω
with a resistance to ground. A 25Ω resistance (RT) is
included on the V− input to get bias current cancellation.
Proper supply bypassing is shown in Figure 2, and
consists of two capacitors on each supply pin: one large
electrolytic capacitor (2.2µF to 6.8µF), effective at lower
frequencies, and one small ceramic capacitor (0.1µF) for
high frequency decoupling. For more information on
decoupling, refer to the Board Layout section.
VI
50Ω
Source
+5V −5V
0.1µF
0.1µF
6.8µF
+
6.8µF
+
6
87
2
RS
50Ω
VCA810
3
5
1
RT
25Ω
RC
RL
500Ω
VO
VC
Figure 2. Variable Gain, Specification and Test
Circuit
Notice that both inverting and non-inverting inputs are
connected to ground with a resistor (RS and RT). Matching
the DC source impedance looking out of each input will
minimize input offset voltage error.
11
11 Page | ||
| Páginas | Total 25 Páginas | |
| PDF Descargar | [ Datasheet VCA810.PDF ] | |
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