參數(shù)資料
型號(hào)： LT1228
廠商： Linear Technology Corporation
英文描述： 100MHz Current Feedback Amplifier with DC Gain Control(100MHz ，電流反饋放大器（帶直流增益控制）)
中文描述： 100MHz的電流反饋放大器的直流增益控制（100MHz時(shí)，電流反饋放大器（帶直流增益控制））
文件頁(yè)數(shù)： 10/20頁(yè)
文件大?。?/td> 357K
代理商： LT1228
LT1228
10
U
S
A
O
PPLICATI
U
U
Substituting into the equation for transconductance gives:
g
a
R
R
m
=
=
1 94
.
10
The temperature variation in the term “a” can be ignored
since it is much less than that of the term “T” in the
equation for V
be
. Using a 2.5V source this way will main-
tain the gain constant within 1% over the full temperature
range of –55
°
C to 125
°
C. If the 2.5V source is off by 10%,
the gain will vary only about
±
6% over the same tempera-
ture range.
We can also temperature compensate the transconduc-
tance without using a 2.5V reference if the negative power
supply is regulated. A Thevenin equivalent of 2.5V is
generated from two resistors to replace the reference. The
two resistors also determine the maximum set current,
approximately 1.1V/R
TH
. By rearranging the Thevenin
equations to solve for R4 and R6 we get the following
equations in terms of R
TH
and the negative supply, V
EE
.
R
R
V
V
andR
R
V
TH
2 5
.
EE
TH EE
2 5
.
4
1
6
=
=
–
Temperature Compensation of g
m
with a Thevenin Voltage
LT1228 TA05
R4
1.24k
–15V
g
m
5
4
R'
I
SET
I
SET
1.03k
V
be
V
be
V
TH
= 2.5V
R'
R6
6.19k
Voltage Controlled Gain
To use a voltage to control the gain of the transconduc-
tance amplifier requires converting the voltage into a
current that flows into pin 5. Because the voltage at pin 5
is two diode drops above the negative supply, a single
resistor from the control voltage source to pin 5 will suffice
in many applications. The control voltage is referenced to
the negative supply and has an offset of about 900mV. The
conversion will be monotonic, but the linearity is deter-
mined by the change in the voltage at pin 5 (120mV per
decade of current). The characteristic is very repeatable
since the voltage at pin 5 will vary less than
±
5% from part
to part. The voltage at pin 5 also has a negative tempera-
ture coefficient as described in the previous section. When
the gain of several LT1228s are to be varied together, the
current can be split equally by using equal value resistors
to each pin 5.
For more accurate (and linear) control, a voltage-to-
current converter circuit using one op amp can be used.
The following circuit has several advantages. The input no
longer has to be referenced to the negative supply and the
input can be either polarity (or differential). This circuit
works on both single and split supplies since the input
voltage and the pin 5 voltage are independent of each
other. The temperature coefficient of the output current is
set by R5.
LT1228 TA19
R5
1k
R1
1M
V1
V2
I
TO PIN 5
OF LT1228
50pF
R1 = R2
R3 = R4
I
OUT
= (V1 – V2)
×
R1
–
+
R2
1M
R3
1M
R4
1M
LT1006
Digital control of the transconductance amplifier gain is
done by converting the output of a DAC to a current flowing
into pin 5. Unfortunately most current output DACs
sink rather than source current and do not have output
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LT1228CN8 功能描述:IC CURRNT FEEDBCK AMP100MHZ 8DIP RoHS:否 類(lèi)別:集成電路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 標(biāo)準(zhǔn)包裝:73 系列:Over-The-Top® 放大器類(lèi)型:通用 電路數(shù):4 輸出類(lèi)型:滿(mǎn)擺幅 轉(zhuǎn)換速率:0.07 V/µs 增益帶寬積:200kHz -3db帶寬:- 電流 - 輸入偏壓:1nA 電壓 - 輸入偏移:285µV 電流 - 電源:50µA 電流 - 輸出 / 通道:25mA 電壓 - 電源，單路/雙路(±):2 V ~ 44 V，±1 V ~ 22 V 工作溫度:-40°C ~ 85°C 安裝類(lèi)型:表面貼裝 封裝/外殼:16-WFDFN 裸露焊盤(pán) 供應(yīng)商設(shè)備封裝:16-DFN-EP（5x3） 包裝:管件
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