FREQUEnCY comPEnSATion CIRCUITS - GEnERAL InFORmATion OPERATionAL AmPLIFIERS VOLTAGE REGULATO

Standard Compensation Circuit

+V'N __ R3 'W---:' R2

RI Co C'<:RI + R2

• Co =30pF

•• BANDWIDTH AND SLEW RATE.ARE PROPORTIONAL TO 1Ie,

Alternate· Frequency Compensation

RI R2

-VIN --''''''' ... p---~ ... - - . . ,

• IMPROVES REJECTION OF POWER SUPPLY NOISE BY A FACTOR OF 5 .

•• BANDWIDTH AND SLEW RATE ARE PROPORTIONAL TO II Cs

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TYPICAL PERFORmAnCE CHARACTERISTICS

Offset Vollage Drift vs Source Resistance

G (Balanced or Unbalanced)

e... 100 SOURCE RESISTANCE (OHMS)

iii 5

-METAL CAN (H)

PACKAGE-/ '

DUAL·IN·LlNE PACKAGE

Offsel Vollage vs Source Reslslance (Balanced or Unbalanced)

I---Vs - ± 15V / SOURCE RESISTANCE (OHMS)

Long Term Slablllty of Four Represenlallve Unlls

Inpul Bias Currenl Over Common Mode Range

Vs - ± 15V

I I

TA - 25'C

DEY'CE WITH POSITIVE INPUT CU~RENT

R,NC", - 2 X, 10"11 DEVICE WITH NEGATIVE INPUT CURRE!iL

-

COMMON·MODE INPUT VOLTAGE

Offsel Vollage Drill with Temperalure of Four Represenlallve Unlls

r-^'-

-

^:---

Supply Currenl vs Supply Vollage Oulpul Shorl Circuli Currenl vs Time

500

TIME FROM OUTPUT SHORT (MINUTES)

TYPICAL PERFORmAnCE CHARACTERISTICS

Voltage Gain vs Frequency

~ ~

Voltaga Gain vs Load Resistanca

10M

LOAD RESISTANCE (k!l)

S' :s

VOLTAGE NOISE 1=1) Cb~I~~R

Gain. Phasa Shill vs Fraquancy with Alternate Compansation

40 GAIN

Cs -10p!

1000

100

1--f-'i--rtttttt--+-++ttI'IoH-'-+t+H-tttl 180 -10 L-.l....l...J..J..l.llU..-1-...J...J..L.Wll-...I.>.l...J..J..J.u.u 200

0.01 0.1 10

FREQUENCY (MHz)

Common Moda ReJaction vs Frequency

140

Total Noise vs Sou rca Reslstanca

10.0 SOURCE RESISTANCE (OHMS)

Gain. Phasa Shill vs Frequancy

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with Standard (Faadback) Compansatlon

40 I'\.

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1-t-++tttttl---+-t+Ittt1 .... H++tttt1180 TA _ 25°C PHASE MARGIN~~

Vs - ± 15V ~11!ci~'

-

^30p!

-10 '--.LJ...J..W.W.!>'-""_~~J....J....ll.L.1.W200

0.01 0.1 1 10

FREQUENCY (MHz)

Power Supply RaJeCtion vs Fraquency

140 r--r-;-:--;:...,--=--,,---,---,-'--,

20'--~-'---L~~-L~~~

0.1 10 100 1k 10k FREQUENCY (Hz)

Large Signal Transient Response

Slew Rate vs Compensation Capacitance

10 Large Signal Transient Response

l\

^VsT, ^~~ ^±15V25'C Cs

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1'-.

I I 1"'-_~ 1 _I

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20 40 60 80 100

Av ~ +1, Cs ~ 100pF, 20~sec/DIV COMPENSATION CAPACITOR (pF) Av ~ + 1, C, ~ 30pF, 20~sec/DIV

Small Signal Transient Response Small Signal Transient Response Small Signal Transient Responsa

Av ~ + 1, Cs ~ 100pF, CLOAD ~ 100pF, 5~sec/DIV Av ~ +1, Cs ~ 100pF, CLDAD ~ 600pF, 5~sec/DlV Av ~ + 1, C, ~ 30pF, CLOAD ~ 100pF, 5~sec/DIV

APPLICATions InFORmATion

Achieving Picoampere/Microvolt Performance

In order to realize the picoampere - microvolt level accuracy of the LT1008, proper care must be exer-cised. For example, leakage currents in circuitry exter-nal to the op amp can significantly degrade performance. High quality insulation should be used (e.g. Teflon, Kel-F); cleaning of all insulating surfaces to remove fluxes and other residues will probably be required. Surface coating may be necessary to pro-vide a moisture barrier in high humidity environments.

Board leakage can be minimized by encircling the in-put circuitry with a guard ring operated at a potential close to that of the inputs: in inverting configurations the guard ring should be tied to ground, in

non-invert-ing connections to the invertnon-invert-ing input at pin 2. Guard-ing both sides of the printed circuit board is required.

Bulk leakage reduction depends on the guard ring width. Nanoampere level leakage into the compensa-tion terminals can affect offset voltage and drift with temperature.

COMPENSATION

V+

I~

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OUTPUT ' 6 7 1

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APPLICATions InFoRmATion

Microvolt level error voltages can also be generated in the external circuitry. Thermocouple effects caused by temperature gradients across dissimilar metals at the contacts to the input terminals can exceed the inher-ent drift of the ampl ifier. Air currinher-ents over device leads should be minimized, package leads should be short, and the two input leads should be as close together as possible and maintained at the same temperature.

The LT1 DOS is specified over a wide range of power-supply voltages from ± 2V to ± 1SV. Operation with lower supplies is possible down to ± 1.0V (two Ni-Cad-batteries) .

Test Circuit for Offset Voltage and its Drift with Temperature

• 50k +15V

100n > - - _ - - V o

• RESISTORS MUST HAVE LOW THERMOELECTRIC POTENTIAL R3

50k -15V

Vo ~ 1000 Vas

•• THIS CIRCUIT IS ALSO USED AS THE BURN-IN CONFIGURATION FOR THE LT100B, WITH SUPPLY VOLTAGES INCREASED TO ± 20V, R1 =R3= 20k R2=200n, Av=100.

Noise Testing

The O.1Hz to 10Hz peak-to-peak noise of the LT100S is measured in the test circuit shown. The frequency re-sponse of this noise tester indicates that the O.1Hz corner is defined by only one zero. The test time to measure O.1Hz to 10Hz noise should not exceed 10 seconds, as this time limit acts as an additional zero to eliminate noise contributions from the frequency band below 0.1 Hz.

O.1Hz to 10Hz Noise Test Circuit

O.1eF

100kn

• LT100B DEVICE UNDER TEST NOTE: ALL CAPACITOR VALUES ARE FOR

A noise-voltage density test is recommended when measuring noise on a large number of units. A 10Hz noise-voltage density measurement will correlate well with a O.1Hz to 10Hz peak-to-peak noise reading since both results are determined by the white noise and the location of the 1 If corner frequency.

Current noise is measured in the circuit shown and calculated by the following formula where the noise of the source resistors is subtracted.

. [e2 no - (S20nV)2]'h

In = 40MQ X 100

10k

10M 10M 100n

10M 10M

• METAL FILM

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APPLICATions InFoRmATion

Frequency Compensation

The LT1008 is externally frequency compensated with a single capacitor. The two standard compensation circuits shown on page 3 are identical to the LM 108A1 308A frequency compensation schemes. Therefore, the LT1008 operational amplifiers can be inserted di-rectly into LM108A/308A sockets, with similar AC and upgraded DC performance.

External frequency compensation provides the user with additional flexibility in shaping the frequency re-sponse of the amplifier. For example, for a voltage gain of ten, and C, = 3pF, a gain bandwidth product of 5MHz and slew rate of 1.2V I ,usec can be realized. For closed loop gains in excess of 200, no external com-pensation is necessary, and slew rate increases to 4V I ,usec. The LT1008 can also be overcompensated (Le. C, > 30pF or Cs > 100pF) to improve capacitive load handling capability or to narrow noise

band-Inverler Feedforward Compensation

C2 5

R1 10k

10k INPUT

-JV1lv-t---C1 500 pF

J

C3 ^{10 PF}

Follower Feedforward Compensation

10k

frffr?>"_-OUTPUT

1000pF

width. In many applications, the feedback loop around the amplifier has gain (e.g. logarithmic amplifiers);

overcompensation can stabilize these circuits with a single capacitor.

The availability of the compensation terminals permits the use of feedforward frequency compensation to en-hance slew rate in low closed loop gain configurations.

The inverter slew rate is increased to 1.4V

l,usec.

The voltage follower feedforward scheme bypasses the amplifier's gain stages and slews at nearly 10V I ,usec.

The inputs of the LT1008 are protected with back-to-back diodes. Current limiting resistors are not used, because the leakage of these resistors would prevent the realization of picoampere level bias currents at ele-vated temperatures. In the voltage follower configura-tion, when the input is driven by a fast, large Signal pulse (> 1V), the input protection diodes effectively short the output to the input during slewing, and a cur-rent, limited only by the output short circuit protection will flow through the diodes.

The use of a feedback resistor, as shown in the voltage follower, feedforward diagram, is recommended be-cause this resistor keeps the current below the short circuit limit, resulting in faster recovery and settling of the output.

5"sec/DlVISION

APPLICATions

Logarithmic Amplifier

01A

+15V 10k'

INPUT -"W'v-...

R1 100k

1~6k ^T

30pF

+ - TEL. LABS, TYPE 081

• - 1% FILM RESISTOR 01 - 2N2979

15.7k-OUTPUT

Amplifier for Bridge Transducers

V+ 56M

1~Jk T

30pF

R3 510k

>,-_-OUTPUT R4

510k

R2 R6

100k 56M

VOLTAGE GAIN

~ 100

"::"

Amplifier For Photodiode Sensor

R1 5M 1%

Vour - 10V/p.A OUTPUT

01B 124k' 5.1k

~--1~---_-""""...--..-"W'v--+15V

1k+

LT1004C 1.2V

"::" Low bias current and offset voltage of the LT100a allow 4112 decades of voltage input logging.

Saturated Standard Cell Amplifier

. - - - _ - + 1 5 V

.4-0UTPUT

The typical30pA bias current of the LT100a will degrade the standard cell by only 1 ppm/year. Noise is a fraction of a ppm. Unprotected gate MOSFET isolates standard cell on power down.

Five Decade Kelvin-Varley Divider Buffered by the LT100B

100k KELVIN·VARLEY

DIVIDER ESI #DP311 00000-99999 + 1

~'--4_ OUTPUT

1000pF

Approximate error due to noise, bias current, common-mode rejection, voltage gain of the amplifier is 1/5 of a least significant bit.

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Extended Range Charge Pump Voltage to Frequency Conv~rter +15V

-15V

ALL DIODES

OPTIONAL 22M .01Hz TRIM

+15V

1.8k 1000pF (POLYSTYRENE)

10k

1N4148 '---"'-'---11---+----O.01Hz to 10kHz

01% METAL FILM RESISTOR 5pF FREQUENCY

OUTPUT

The LT1008 integrator extends low frequency range. Total

dynamic range is 0.01Hz to 10kHz (or 120dB) with 0.01% linearity.

Precision, Fast Settling, Low Pass Filter

2k INPUT--... NV-... ...,

o OPTO-MOS SWITCH TYPE OFM1A THETA-J CORP.

10k

Ii&>--... --OUTPUT

This circuit is useful where fast signal acquisition and high precision are required, as in electronic scales.

The filter's time constant is set by the 2Kn resistor and the 1",F capacitor until comparator #1 switches.

The time constant is then set by the 1.5Mn resistor and the 1",F capacitor. Comparator #2 provides a quick reset.

The circuit settles to a final value three times as fast as a simple 1.5Mn - 1",F filter, with almost no DC error.

Fast Precision Inverters

INPUT 10k

1N4148

10k' INPUT

-15V 1N4148 (4)

10k

6 OUTPUT

SLEW RATE @ 100V I"S

300pF +15V

30pF

SETTLING ~ 5"S TO .01%/10 VOLT STEP OFFSET VOLTAGE ~ 30"V

Ammeter With Six Decade Range

CURRENT INPUT

01,02,03, 04, RCA CA3146 TRANSISTOR ARRAY.

CALIBRATION: ADJUST R1 FOR FULL SCALE DEFLECTION WITH 1"A INPUT CURRENT.

BIAS CURRENT ~ 30pA '1% METAL FILM

10k

Ammeter measures currents from 100pA to 100}LA without the use of expensive high value resistors. Ac-curacy at 100}LA is limited by the offset voltage be-tween 01 and 02 and, at 100pA, by the inverting bias

10pA

*1 % METAL FILM

R1 2k 1.2k 549!l

549!l 54911 54911 54911 54911

10pF

+15V

10k -15V

FULL POWER BANDWIDTH ~ 2MHz SLEW RATE ~ 50V I "sec

SETTLING (10V STEP) ~ 12"S TO 0.01%

BIAS CURRENT DC ~ 30pA OFFSET DRIFT ~ 0.3"V lOG OFFSET VOLTAGE ~ 30"V

10k +15V

LT 1004C-1.2

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SCHEmATIC DIAGRAm

Dans le document GEnERAL InFORmATion OPERATionAL AmPLIFIERS VOLTAGE REGULATORS VOLTAGE REFEREnCES comPARATORS (Page 78-87)