參數(shù)資料
型號: LM359M
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類: 運(yùn)動控制電子
英文描述: Dual, High Speed, Programmable, Current Mode Norton Amplifiers
中文描述: DUAL OP-AMP, 30 MHz BAND WIDTH, PDSO14
封裝: PLASTIC, SOP-14
文件頁數(shù): 12/24頁
文件大?。?/td> 742K
代理商: LM359M
Application Hints
(Continued)
DESIGN EXAMPLE:
e
= 50 mV (MAX), f
= 10 MHz (MAX), desired circuit
BW = 20 MHz, A
V
= 20 dB, driving source impedance =
75
, V
+
= 12V.
1.
Basic circuit configuration:
2.
Select I
to provide adequate amplifier bandwidth so
that the closed loop bandwidth will be determined by R
f
and C
. To do this, the set current should program an
amplifier open loop gain of at least 20 dB at the desired
closed loop bandwidth of the circuit. For this example,
an I
of 0.5 mA will provide 26 dB of open loop gain at
20 MHz which will be sufficient. Using single resistor pro-
gramming for I
SET
:
3.
Since the closed loop bandwidth will be determined by
to obtain a 20 MHz bandwidth, both R
and C
should be kept
small. It can be assumed that C
can be in the range of 1 pF
to 5 pF for carefully constructed circuit boards to insure sta-
bility and allow a flat frequency response. This will limit the
value of R
f
to be within the range of:
Also, for a closed loop gain of +10, R
must be 10 times R
s
+ r
e
where r
e
is the mirror diode resistance.
4.
So as not to appreciably load the 75
input termination
resistance the value of (R
s
+ r
e
) is set to 750
.
5.
For A
v
= 10; R
f
is set to 7.5 k
.
6.
The optimum output DC level for symmetrical AC swing
is:
7.
The DC feedback current must be:
DC biasing predictability will be insured because 640 μA is
greater than the minimum of I
/5 or 100 μA.
For gain accuracy the total AC and DC mirror current should
be less than 2 mA. For this example the maximum AC mirror
current will be:
therefore the total mirror current range will be 574 μA to 706
μA which will insure gain accuracy.
8.
R
b
can now be found:
9.
Since R
+ r
will be 750
and r
e
is fixed by the DC mir-
ror current to be:
R
must be 750
–40
or 710
which can be a 680
resis-
tor in series with a 30
resistor which are standard 5% toler-
ance resistor values.
10. As a final design step, C
must be selected to pass the
lower passband frequency corner of 8 Hz for this ex-
ample.
A larger value may be used and a 0.01 μF ceramic capacitor
in parallel with C
i
will maintain high frequency gain accuracy.
DS007788-20
www.national.com
12
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