–VEE REF GND BIPOLAR OFFSE" />
參數(shù)資料
型號(hào): AD744KRZ-REEL7
廠商: Analog Devices Inc
文件頁(yè)數(shù): 2/12頁(yè)
文件大?。?/td> 0K
描述: IC OPAMP BIFET 13MHZ PREC 8SOIC
標(biāo)準(zhǔn)包裝: 1,000
放大器類型: J-FET
電路數(shù): 1
轉(zhuǎn)換速率: 75 V/µs
-3db帶寬: 13MHz
電流 - 輸入偏壓: 30pA
電壓 - 輸入偏移: 250µV
電流 - 電源: 3.5mA
電流 - 輸出 / 通道: 25mA
電壓 - 電源,單路/雙路(±): ±4.5 V ~ 18 V
工作溫度: 0°C ~ 70°C
安裝類型: 表面貼裝
封裝/外殼: 8-SOIC(0.154",3.90mm 寬)
供應(yīng)商設(shè)備封裝: 8-SOIC
包裝: 帶卷 (TR)
REV. C
AD744
–10–
19.95k
20k
9.96k
5k
8k
20V SPAN
10V SPAN
DAC OUT
POWER
GND
–VEE
REF
GND
BIPOLAR
OFFSET
ADJUST
5k
LSB
MSB
10V
VCC
REF
OUT
REF
IN
0.1 F
100
AD744
1 F
+15V
1 F
CLEAD
10pF
–15V
100
GAIN
ADJUST
AD565A
Figure 34.
±10 V Voltage Output Bipolar DAC Using the AD744 as an Output Buffer
HIGH-SPEED OP AMP APPLICATIONS
AND TECHNIQUES
DAC Buffers (I-to-V Converters)
Digital-to-analog converters which use bipolar transistors to
switch currents into (or out of) their outputs can achieve very
fast settling times. The AD565A, for example, is specified to
settle to 12 bits in less than 250 ns, with a current output. How-
ever, in many applications, a voltage output is desirable, and it
would be useful – perhaps essential – that this I-to-V conversion
be accomplished without increasing the settling time or without
degrading the accuracy of the DAC.
Figure 34 is a schematic of an AD565A DAC using an AD744
output buffer. The 10 pF CLEAD capacitor compensates for the
DAC’s output capacitance, plus the 5.5 pF amplifier input
capacitance.
Figure 35 is an oscilloscope photo of the AD744’s output volt-
age with a +10 V to 0 V step applied; this corresponds to an all
“1s” to all “0s” code change on the DAC. Since the DAC is
Figure 35. Upper Trace: AD744 Output Voltage for
a +10 V to 0 V Step, Scale: 5 mV/div.
Lower Trace: Logic Input Signal, Scale: 5 V/div.
connected in the 20 V span mode, 1 LSB is equal to 4.88 mV.
Output settling time for the AD565/AD744 combination is less
than 500 ns to within a 2.44 mV, 1/2 LSB error band.
A HIGH-SPEED, 3 OP AMP INSTRUMENTATION
AMPLIFIER CIRCUIT
The instrumentation amplifier circuit shown in Figure 36 can
provide a range of gains from unity up to 1000 and higher. The
circuit bandwidth is 4 MHz at a gain of 1 and 750 kHz at a gain
of 10; settling time for the entire circuit is less than 2
s
to within 0.01% for a 10 V step, (G = 10).
While the AD744 is not stable with 100% negative feedback (as
when connected as a standard voltage follower), phase margin
and therefore stability at unity gain may be increased to an accept-
able level by placing the parallel combination of a resistor and a
small lead capacitor between each amplifier’s output and its
inverting input terminal.
The only penalty associated with this method is a small band-
width reduction at low gains. The optimum value for CLEAD
may be determined from the graph of Figure 41. This technique
can be used in the circuit of Figure 36 to achieve stable opera-
tion at gains from unity to over 1000.
AD744
+VS
1 F
+15V
COMM
–15V
–VS
1 F
0.1 F
PIN 7
PIN 4
EACH
AMPLIFIER
A1
–IN
10k
7.5pF
**10k
AD744
A3
7.5pF
**10k
5pF
**10k
*1.5pF – 20pF
(TRIM FOR BEST SETTLING TIME)
SENSE
10k
AD744
A2
+IN
REFERENCE
*VOLTRONICS SP20 TRIMMER CAPACITOR OR EQUIVALENT
**RATIO MATCHED 1% METAL FILM RESISTORS
20,000
RG
CIRCUIT GAIN =
+ 1
FOR OPTIONAL OFFSET ADJUSTMENT:
TRIM A1, A3 USING TRIM PROCEDURE SHOWN IN FIGURE 21.
RG
Figure 36. A High Performance, 3 Op Amp
Instrumentation Amplifier Circuit
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