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Teilenummer | AD830 |
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Beschreibung | High Speed Video Difference Amplifier | |
Hersteller | Analog Devices | |
Logo | ||
Gesamt 21 Seiten FEATURES
Differential amplification
Wide common-mode voltage range: +12.8 V to −12 V
Differential voltage: ±2 V
High CMRR: 60 dB at 4 MHz
Built-in differential clipping level: ±2.3 V
Fast dynamic performance
85 MHz unity gain bandwidth
35 ns settling time to 0.1%
360 V/μs slew rate
Symmetrical dynamic response
Excellent video specifications
Differential gain error: 0.06%
Differential phase error: 0.08°
15 MHz (0.1 dB) bandwidth
Flexible operation
High output drive of ±50 mA min
Specified with both ±5 V and ±15 V supplies
Low distortion: THD = −72 dB @ 4 MHz
Excellent DC performance: 3 mV max input
Offset voltage
APPLICATIONS
Differential line receiver
High speed level shifter
High speed in-amp
Differential to single-ended conversion
Resistorless summation and subtraction
High speed analog-to-digital converter
GENERAL DESCRIPTION
The AD830 is a wideband, differencing amplifier designed for use
at video frequencies but also useful in many other applications. It
accurately amplifies a fully differential signal at the input and
produces an output voltage referred to a user-chosen level. The
undesired common-mode signal is rejected, even at high
frequencies. High impedance inputs ease interfacing to finite
source impedances and, thus, preserve the excellent common-
mode rejection. In many respects, it offers significant
improvements over discrete difference amplifier approaches, in
particular in high frequency common-mode rejection.
The wide common-mode and differential voltage range of the
AD830 make it particularly useful and flexible in level shifting
applications but at lower power dissipation than discrete solutions.
Low distortion is preserved over the many possible differential and
common-mode voltages at the input and output.
Rev. C
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
High Speed, Video
Difference Amplifier
AD830
CONNECTION DIAGRAM
X1 1
X2 2
Y1 3
Y2 4
GM AD830 8 VP
A=1
7 OUT
6 NC
GM C
5 VN
NC = NO CONNECT
Figure 1. 8-Lead Plastic PDIP (N), CERDIP (Q), and SOIC (RN) Packages
110
100
90
80
VS = ±15V
70
60
VS = ±5V
50
40
30
1k
10k 100k
FREQUENCY (Hz)
1M
10M
Figure 2. Common-Mode Rejection Ratio vs. Frequency
Good gain flatness and excellent differential gain of 0.06% and
phase of 0.08° make the AD830 suitable for many video system
applications. Furthermore, the AD830 is suited for general-purpose
signal processing from dc to 10 MHz.
9 VS = ±5V
6 RL = 150Ω
3
CL = 33pF
0
–3
CL = 4.7pF
–6
–9
–12
CL = 15pF
–15
–18
–21
10k 100k 1M 10M 100M
FREQUENCY (Hz)
Figure 3. Closed-Loop Gain vs. Frequency, Gain = +1
1G
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113 ©2005–2010 Analog Devices, Inc. All rights reserved.
AD830
VS = ±5 V, RLOAD = 150 Ω, CLOAD = 5 pF, TA = +25°C, unless otherwise noted.
Table 2.
Parameter
DYNAMIC CHARACTERISTICS
3 dB Small Signal Bandwidth
0.1 dB Gain Flatness Frequency
Differential Gain Error
Differential Phase Error
Slew Rate, Gain = +1
3 dB Large Signal Bandwidth
Settling Time
Harmonic Distortion
Input Voltage Noise
Input Current Noise
DC PERFORMANCE
Offset Voltage
Open-Loop Gain
Unity Gain Accuracy
Peak Nonlinearity, RL= 1 kΩ
Input Bias Current
Input Offset Current
INPUT CHARACTERISTICS
Differential Voltage Range
Differential Clipping Level2
Common-Mode Voltage Range
CMRR
Input Resistance
Input Capacitance
OUTPUT CHARACTERISTICS
Output Voltage Swing
Short-Circuit Current
Output Current
Conditions
Gain = +1, VOUT = 100 mV rms
Gain = +1, VOUT = 100 mV rms
0 V to 0.7 V, frequency = 4.5 MHz,
Gain = +2
0 V to 0.7 V, frequency = 4.5 MHz,
Gain = +2
2 V step, RL = 500 Ω
4 V step, RL = 500 Ω
Gain = +1, VOUT = 1 V rms
VOUT = 2 V step, to 0.1%
VOUT = 4 V step, to 0.1%
2 V p-p, frequency = 1 MHz
2 V p-p, frequency = 4 MHz
Frequency = 10 kHz
Gain = +1
Gain = +1, TMIN − TMAX
DC
RL = 1 kΩ
−1 V ≤ X ≤ +1 V
−1.5 V ≤ X ≤ +1.5 V
−2 V ≤ X ≤ +2 V
VIN = 0 V, 25°C to TMAX
VIN = 0 V, TMIN
VIN = 0 V, TMIN − TMAX
VCM = 0
Pin 1 and Pin 2 inputs only
VDM = ±1 V
DC, Pin 1/Pin 2, +4 V to −2 V
DC, Pin 1/Pin 2, +4 V to −2 V,
TMIN − TMAX
Frequency = 4 MHz
RL ≥ 150 Ω
RL ≥ 150 Ω, ±4 VS
Short to ground
AD830J/AD830A
Min Typ
Max
35 40
5 6.5
0.14
0.32
210
240
30 36
35
48
−69
−56
27
1.4
0.18
0.4
±1.5
60 65
±0.1
0.01
0.045
0.23
5
7
0.1
±3
±4
±0.6
0.03
0.07
0.4
10
13
1
±2.0
±2.0 ±2.2
−2.0
90 100
88
55 60
370
2
+2.9
±3.2 ±3.5
±2.2 −2.4/+2.7
−55/+70
±40
AD830S 1
Min Typ
Max
35 40
5 6.5
0.14
0.32
210
240
30 36
35
48
−69
−56
27
1.4
0.18
0.4
±1.5
60 65
±0.1
0.01
0.045
0.23
5
8
0.1
±3
±5
±0.6
0.03
0.07
0.4
10
17
1
±2.0
±2.0 ±2.2
−2.0
90 100
86
55 60
370
2
+2.9
±3.2 ±3.5
±2.2 −2.4/+2.7
−55/+70
±40
Units
MHz
MHz
%
Degrees
V/μs
V/μs
MHz
ns
ns
dBc
dBc
nV/√Hz
pA/√Hz
mV
mV
dB
%
% FS
% FS
% FS
μA
μA
μA
V
V
V
dB
dB
dB
kΩ
pF
V
V
mA
mA
Rev. C | Page 5 of 20
6 Page AD830
THEORY OF OPERATION
TRADITIONAL DIFFERENTIAL AMPLIFICATION
In the past, when differential amplification was needed to reject
common-mode signals superimposed with a desired signal,
most often the solution used was the classic op amp based
difference amplifier shown in Figure 24. The basic function
VO = V1 − V2 is simply achieved, but the overall performance is
poor and the circuit possesses many serious problems that make
it difficult to realize a robust design with moderate to high
levels of performance.
R1
V2
R2
R3
V1
VOUT
ONLY IF R1 = R2 = R3 = R4
R4 DOES VOUT = V1 – V2
Figure 24. Op Amp Based Difference Amplifier
PROBLEMS WITH THE OP AMP BASED APPROACH
• Low common-mode rejection ratio (CMRR)
• Low impedance inputs
• CMRR highly sensitive to the value of source R
• Different input impedance for the + and − input
• Poor high frequency CMRR
• Requires very highly matched resistors, R1 to R4, to achieve
high CMRR
• Halves the bandwidth of the op amp
• High power dissipation in the resistors for large common-
mode voltage
AD830 FOR DIFFERENTIAL AMPLIFICATION
The AD830 amplifier was specifically developed to solve the
listed problems with the discrete difference amplifier approach.
Its topology, discussed in detail in the Understanding the AD830
Topology section, by design acts as a difference amplifier. The
circuit of Figure 25 shows how simply the AD830 is configured
to produce the difference of the two signals, V1 and V2, in which
the applied differential signal is exactly reproduced at the
output relative to a separate output common. Any common-
mode voltage present at the input is removed by the AD830.
V1 V → I
V2
IX
IY
V→I
A=1
VOUT
VOUT = V1 – V2
Figure 25. AD830 as a Difference Amplifier
ADVANTAGEOUS PROPERTIES OF THE AD830
• High common-mode rejection ratio (CMRR)
• High impedance inputs
• Symmetrical dynamic response for +1 and −1 Gain
• Low sensitivity to the value of source R
• Equal input impedance for the + and − input
• Excellent high frequency CMRR
• No halving of the bandwidth
• Constant power distortion versus common-mode voltage
• Highly matched resistors not needed
UNDERSTANDING THE AD830 TOPOLOGY
The AD830 represents Analog Devices first amplifier product to
embody a powerful alternative amplifier topology. Referred to
as active feedback, the topology used in the AD830 provides
inherent advantages in the handling of differential signals,
differing system commons, level shifting, and low distortion,
high frequency amplification. In addition, it makes possible the
implementation of many functions not realizable with single op
amp circuits or superior to op amp based equivalent circuits.
With this in mind, it is important to understand the internal
structure of the AD830.
The topology, reduced to its elemental form, is shown in Figure 26.
Nonideal effects, such as nonlinearity, bias currents, and limited
full scale, are omitted from this model for simplicity but are
discussed later. The key feature of this topology is the use of
two, identical voltage-to-current converters, GM, that make up
input and feedback signal interfaces. They are labeled with
inputs VX and VY, respectively. These voltage-to-current
converters possess fully differential inputs, high linearity, high
input impedance, and wide voltage range operation. This
enables the part to handle large amplitude differential signals; it
also provides high common-mode rejection, low distortion, and
negligible loading on the source. The label, GM, is meant to
convey that the transconductance is a large signal quantity,
unlike in the front end of most op amps. The two GM stage
current outputs, IX and IY, sum together at a high impedance
node, which is characterized by an equivalent resistance and
capacitance connected to an ac common. A unity voltage gain
stage follows the high impedance node to provide buffering
from loads. Relative to either input, the open-loop gain, AOL, is
set by the transconductance, GM, working into the resistance,
RP; AOL = GM × RP. The unity gain frequency, ω0 dB, for the open-
loop gain is established by the transconductance, GM, working
into the capacitance, CC; ω0 dB = GM/CC. The open-loop
description of the AD830 is shown below for completeness.
Rev. C | Page 11 of 20
12 Page | ||
Seiten | Gesamt 21 Seiten | |
PDF Download | [ AD830 Schematic.PDF ] |
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