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| 型號： | VCA810IDR |
| 英文描述： | High Gain Adjust Range, Wideband, Voltage-Controlled Amplifier |
| 中文描述： | 高增益調(diào)整范圍，寬帶，電壓控制放大器 |
| 文件頁數(shù)： | 21/25頁 |
| 文件大小： | 417K |
| 代理商： | VCA810IDR |
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SBOS275C JUNE 2003 REVISED OCTOBER 2004
www.ti.com
21
shown in Figure 19. R
P
should be no greater than 100
so
as not to introduce gain errors by interacting with the gain
control input bias current of 6
μ
A.
VCA610
V
O
R
P
C
P
V
C
f
3dB
1
2 R
P
C
P
Figure 19. Control Line Filtering
GAIN CONTROL AND TEEPLE POINT
When the VCA810 controlled voltage reaches 1.5V, also
referred to as the Teeple point, the signal path undergoes
major changes. From 0V to the Teeple point, the gain is
controlled by one bank of amplifiers: a low-gain VCA. As
the Teeple point is passed, the signal path is switched to
a higher gain VCA. This gain-stage switching can be seen
most clearly in the
Noise Density vs Control Voltage
Typical Characteristics curve. The output-referred voltage
noise density increases proportionally to the control
voltage and reaches a maximum value at the Teeple point.
As the gain increases and the internal stages switch, the
output-referred voltage noise density drops suddenly and
restarts its proportional increase with the gain.
NOISE PERFORMANCE
The VCA810 offers 2.4nV/
√
Hz input-referred voltage
noise and 1.8 pA/
√
Hz input-referred current noise at a gain
of +40dB. The input-referred voltage noise, and the
input-referred current noise terms, combine to give low
output noise under a wide variety of operating conditions.
Figure 20 shows the op amp noise analysis model with all
the noise terms included. In this model, all noise terms are
taken to be noise voltage or current density terms in either
nV/
√
Hz or pA/
√
Hz.
R
T
VCA810
5V
E
O
V
C
I
BI
+5V
R
S
I
BN
E
NI
E
RS
4kTR
S
*
*
*
4kTR
T
Figure 20. VCA810 Noise Analysis Model
The total output spot noise voltage can be computed as the
square root of the sum of all squared output noise voltage
contributors. Equation (8) shows the general form for the
output noise voltage using the terms shown in Figure 20.
E
O
G
V V
E
2
NI
I
BI
R
T
2
I
BN
R
S
2
4kT R
S
R
T
Dividing this expression by the gain will give the equivalent
input-referred spot-noise voltage at the non-inverting input
as shown by Equation (9).
E
N
E
2
NI
I
BI
R
T
2
I
BN
R
S
2
4kT R
S
R
T
Evaluating these two equations for the VCA810 circuit and
component values shown in Figure 2 (maximizing gain)
will give a total output spot-noise voltage of 272.3nV
√
Hz
and a total equivalent input-referred spot-noise voltage of
2.72nV
√
Hz. This total input-referred spot-noise voltage is
higher than the 2.4nV
√
Hz specification for the VCA810
alone. This reflects the noise added to the output by the
input current noise times the input resistance R
S
and R
T
.
Keeping input impedance low is required to maintain low
total equivalent input-referred spot-noise voltage.
THERMAL ANALYSIS
The VCA810 will not require heatsinking or airflow in most
applications. Maximum desired junction temperature
would set the maximum allowed internal power dissipation
as described in this section. In no case should the
maximum junction temperature be allowed to exceed
+150 C.
Operating junction temperature (T
J
) is given by
T
J
T
A
P
D
JA
.
The total internal power dissipation (P
D
) is the sum of
quiescent power (P
DQ
) and additional power dissipated in
the output stage (P
DL
) to deliver load power. Quiescent
power is simply the specified no-load supply current times
the total supply voltage across the part. P
DL
depends on
the required output signal and load; for a grounded
resistive load, however, it is at a maximum when the output
is fixed at a voltage equal to one-half of either supply
voltage (for equal bipolar supplies). Under this worst-case
condition, P
DL
= V
S2
/(4
R
L
), where R
L
is the resistive
load.
Note that it is the power in the output stage and not in the
load that determines internal power dissipation. As a
worst-case example, compute the maximum T
J
using an
VCA810ID (SO-8 package) in the circuit of Figure 2
operating at maximum gain and at the maximum specified
ambient temperature of +85
°
C.
P
D
= 10V(24.8mA) + 5
2
/(4
500
) = 260.5mW
Maximum T
J
= +85
°
C + (0.260W
125 C/W) = 117.6
°
C
(8)
(9)
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|---|---|
| VCA810IDRG4 | 功能描述:特殊用途放大器 High-Gain Adj Range Wideband Vltg-Cntrl RoHS:否 制造商:Texas Instruments 通道數(shù)量:Single 共模抑制比（最小值）: 輸入補(bǔ)償電壓: 工作電源電壓:3 V to 5.5 V 電源電流:5 mA 最大功率耗散: 最大工作溫度:+ 70 C 最小工作溫度:- 40 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-20 封裝:Reel |
| VCA811IDR | 制造商:Texas Instruments 功能描述:VCA811: HIGH GAIN ADJUST RANGE, WIDEBAND, VOLTAGE-CONTROLLE - Tape and Reel |
| VCA820 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:Wideband, > 40dB Gain Adjust Range, Linear in V/V VARIABLE GAIN AMPLIFIER |
| VCA-8206 | 制造商:Quest Technology International Inc 功能描述: |
| VCA820ID | 功能描述:特殊用途放大器 150MHz BW w/ Linear RoHS:否 制造商:Texas Instruments 通道數(shù)量:Single 共模抑制比（最小值）: 輸入補(bǔ)償電壓: 工作電源電壓:3 V to 5.5 V 電源電流:5 mA 最大功率耗散: 最大工作溫度:+ 70 C 最小工作溫度:- 40 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-20 封裝:Reel |
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