October 1996 - Linear Technology

Linear Technology Chronicle •

October 1996

A Showcase of Linear Technology’s Focus Products

Linear Technology Chronicle

October 1996 Vol. 5 No. 10

Products of the Month

, LTC and LT are registered trademarks of Linear Technology Corporation.

High Speed Parallel 12-Bit ADCs Deliver on

Performance While Consuming Only Milliwatts

Low Power Quad 12-Bit Rail-to-Rail DACs Have DNL of Only ±0.5LSB................................ 2

An Open-Architecture Ring-Tone Generator .......................................................................... 3

Inductorless Switched Capacitor Converter Delivers 60mA at 12V from 5V Source .............. 4

Quad C-LoadTM JFET Op Amps Offer Power Savings and Picoampere Inputs ...................... 4

Inside This Issue:

C-Load is a trademark of Linear Technology Corporation.

The 1.25Msps LTC

1415 and 800ksps

LTC1409 are 12-bit ADCs with wideband

sample-and-holds and precision references

that consume minimal amounts of power.

The LTC1415 has 72dB signal-to-(noise +

distortion) ratio (SINAD) and 80dB THD at

an input frequency of 100kHz. It operates off

a single 5V supply and dissipates only

55mW (typ) while converting at 1.25Msps.

The LTC1409 has a guaranteed AC perfor-

mance of 71dB SINAD and 82dB THD at

the Nyquist input frequency of 400kHz over

temperature. It accepts ±2.5V inputs and

dissipates only 80mW (typ) while converting

at 800ksps. In sleep mode, these ADCs con-

sume just 10µW and in nap mode only

7.5mW and 4mW, respectively. They

recover from nap mode in 200ns allowing

reduced power consumption during brief

inactive periods. DC specifications include a

maximum INL and DNL of ±1LSB over

temperature. Figure 2 shows the excellent

typical DNL performance for the LTC1415.

The LTC1409 and LTC1415 excel in

applications that must digitize fast moving

signals with outstanding spectral purity. The

sample-and-hold has a high impedance dif-

ferential input that rejects wideband

common mode noise by 60dB, simplifying

front-end signal conditioning design. The

internal precision references can be used for

external circuitry or overridden by an exter-

nal source to improve temperature or time

stability. The three-state parallel interface

easily connects to popular DSP and micro-

processor parallel ports.

The LTC1409 and LTC1415 do not

have a pipeline delay such as found with

multistep architectures. Each conversion

cycle yields results that correlate to the ana-

log input at the time the sample command

was issued. This is a big advantage for mul-

tiplexed process control and robotics

applications or for event capture systems.

They are also ideally suited for demanding

telecom, IF down conversion, undersampling

and high speed data acquisition applications.

Low power dissipation permits use in

battery-powered and portable applications.

The LTC1415 joins the 1.25Msps

LTC1410, introduced last year as LTC’s

fastest 12-bit high speed parallel A/D con-

verter. This growing family of ADCs is

offered in 28-lead SW packages and has

similar pinouts, allowing a single layout to

accommodate any of the three devices. For a

data sheet and evaluation samples of each of

these high performance ADCs, contact your

local Linear Technology sales office.

Figure 1. LTC1409 Has 71dB SINAD at

the Nyquist Input Frequency of 400kHz

INPUT FREQUENCY (Hz)

EFFECTIVE BITS

S/(N + D) (dB)

10k 100k 1M 10M

LTC1409 • TA02

01k

12 74

NYQUIST

FREQUENCY

SAMPLE

= 800ksps

CODE

DNL EOC ERROR (LSB)

4095

1415 TA02

1024 2048 3072

1.0

0.5

0

–0.5

–1.0 512 1536 2560 3584

Figure 2. LTC1415 Has a Typical

Differential Nonlinearity (DNL)

of Only 0.25LSB

Continued on page 2

Low Power 8th Order

Elliptic Lowpass Filter in

SO-8 Needs Only 3V

Supply

The LTC1069-6 is a low power 8th

order, elliptic lowpass filter optimized for

single 3V or 5V supply operation. The low

supply voltage operation of the LTC1069-6

does not penalize dynamic range. It achieves

a 79dB signal-to-noise ratio (S/N) and a cut-

off frequency of 20kHz under 5V operation,

while drawing just 1.2mA (typ) of supply

current. With a single 3V supply, it has a

14kHz cutoff frequency, a 72dB S/N and

typically draws just 1mA of supply current.

No external components are required except

for power supply bypass capacitors.

Cutoff frequency is clock tunable and

equals the clock frequency divided by 50.

The input signal is sampled twice per clock

cycle to lower the risk of aliasing. The

stopband attenuation has a progressive ellip-

tic response reaching 42dB attenuation at 1.3

× fCUTTOFF, 66dB at 2.0 × fCUTTOFF, and

over 70dB at 2.1 × fCUTTOFF. The gain at

fCUTOFF is –0.07dB and typical passband

Linear Technology Chronicle •

October 1996

LTC1069-6 from page 1

ripple is only ±0.1dB. Figure 1 shows the 3V

frequency response of the LT1069-6 for a

500mVRMS input. Figure 2 shows the

dynamic range under 5V operation. These

features make it a good choice for precision

telecommunications and antialiasing applica-

tions, or other filter applications where a

compact solution is required.

The LTC1069-6 is immediately avail-

able in volume from stock in an SO-8

surface mount package over the commercial

and industrial temperature ranges. Contact

your local Linear Technology sales office for

a data sheet and evaluation samples.

Figure 1. Frequency Response of

LTC1069-6 10kHz Elliptic Lowpass Filter

with Single 3V Supply

FREQUENCY (kHz)

–80

GAIN (dB)

–70

–50

–40

–30

LTC1069-6 • TA02

–60

10 20 25

–20

–10

= 500mV

RMS

INPUT VOLTAGE (V

RMS

)

0.1

–85

THD + NOISE (dB)

LTC1069-6 • TA03

= 1kHz

= 5kHz

–45

–50

–55

–60

–65

–70

–75

–80

Figure 2. THD + Noise Characteristics of

LTC1069-6 with 5V Supply

Low Power Quad 12-Bit

Rail-to-Rail DACs Have

DNL of Only ±0.5LSB

The LTC1458/LTC1458L are quad

12-bit DACs, complete with rail-to-rail

amplifiers and references for single 5V and

3V supply applications. They have a maxi-

mum differential nonlinearity (DNL) of only

±0.5LSB for guaranteed 12-bit monotonic

performance. The 5V LTC1458, shown in

Figure 1, typically draws just 1100µA while

the 3V LTC1458L draws only 800µA. They

are ideal in feedback loops of digital control

systems, such as calibration DACs in indus-

trial control systems and for large distributed

power supplies, where multiple inexpensive

D/A devices are required. Their low power

consumption also make them suitable in por-

table battery-powered digitally controlled

instruments where minimal power dissipa-

tion is key.

The LTC1458/58L include an output

buffer amplifier with variable gain (×1 or

×2) and 3-wire serial interface, which is SPI,

QSPI and MICROWIRE

compatible. The

serial interface eases the connection to

microcontrollers and microprocessors with

built-in SPI ports and reduces I/O lines in

remote or isolated applications. The rail-to-

rail amplifiers ensure an accurate full-scale

output even when driving heavy loads on

reduced supply voltages and have improved

capacitive load handling when compared to

competing devices. Power-on reset ensures

that the outputs are at zero scale when pow-

ered up.

The on-chip reference (2.048V for the

LTC1458; 1.220V for LTC1458L) is

brought out, allowing it to be used for exter-

nal circuitry and is not internally connected.

This allows a user specified external refer-

ence to be used for all DACs. The

asynchronous Clear pin resets all DACs to

zero scale on command. This can be useful

in system initialization and interrupt process-

ing schemes. The ability to select the output

amplifiers gain and output ground reference

allows virtually any output range within the

constraints of the power supply. Figure 2

shows the DNL characteristics of the

LTC1458.

The LTC1458/58L are offered in 28-pin

SO and SSOP packages. Both devices are

available from stock screened to the com-

mercial and industrial temperature. Call your

local Linear Technology sales office for a

data sheet and evaluation samples.

1458 BD01

48-BIT

SHIFT REGISTER

AND

DAC REGISTER

CLK D

5V (LTC1458)

3V TO 5V (LTC1458L)

2.048V (LTC1458)

1.22V (LTC1458L)

REFHI C

REFOUT

OUT C

REFLO C

X1/X2 C

X1/X2 D X1/X2 A

X1/X2 B

REFHI D

OUT D

REFLO D

REFHI B

FROM µP

OUT B

REFLO B

REFHI A

OUT A

REFLO A

OUT

CS/LD

CLR

DAC D

DAC C DAC B

DAC A

Figure 1. Functional Block Diagram: Quad 12-Bit

Rail-to-Rail DAC Figure 2. Differential Nonlinearity vs

Input Code for LTC1458—Max DNL is

Less Than ±0.5LSB

CODE

DNL (LSB)

0.5

0.4

0.3

0.2

0.1

0

–0.1

–0.2

–0.3

–0.4

–0.5 1024 2048 2560

1458 G09

512 1536 3072 3584 4095

MICROWIRE is a trademark of National Semiconductor Corp.

Linear Technology Chronicle •

October 1996

Application of the Month

An Open-Architecture Ring-Tone Generator

When a phone rings, it rings with a

cadence, a sequence of rings and pauses.

The standard cadence is one second ring-

ing followed by two seconds of silence.

We use the first 1/4 of an LT

1491 as a

cadence oscillator, whose output is at

for one second and then at V

for

two seconds. This sequence repeats every

three seconds, producing the all-too-

familiar pattern. The actual ringing of the

bell is done by a 20Hz AC sine wave sig-

nal at a signal level of 87V

RMS

superimposed on –48VDC. The 20Hz

signal is implemented with the second

amplifier in the LT1491 which acts as a

gated 20Hz oscillator (see Figure 1).

The third amplifier in the LT1491,

which is configured as a lowpass filter, con-

verts the square wave output of the

oscillator to a sine wave by filtering out

unwanted harmonics. Finally, the 87V

RMS

and the –48VDC parts are handled by the

fourth amplifier in the LT1491 and its steer-

ing of two external 15V regulators.

The rest of what we do, the part that is

most difficult to follow, involves the output

amplifier. In the output amplifier, the 6V

P-P

signal from the waveform synthesizer is

imposed across R12 (see Figure 2) into a

virtual ground, creating a sine wave signal

current. This current is added to the DC cur-

rent flowing through R15 and the resulting

current is imposed across R13. This stage

amplifies the sine wave and offsets it to

become an 87V

RMS

sine wave imposed

on a –48VDC bias. The trick here is that

the voltage gain is in the ±15V regulators,

not the LT1491 which is merely steering

currents.

This complete circuit (Figure 2)

includes the ring-trip sense circuit to

detect when the phone receiver is picked

up. This circuit is fully protected for out-

put shorts to any voltage within the power

supply window of –180V to 60V.

–

F F

DN134 F03

100K 10k

620k10k

16k

1.6M

47k 33k

620k

300k 150k

0.068

V–

0.47

1N4148

1µF

LT1491

0.47

REPRESENTS FLOATING GROUND

NOT EQUAL TO

LT1491 GATED

SINE WAVE

OUTPUT

LT1491

Figure 1. Waveform Synthesizer

Figure 2. Complete Ring-Tone Generator Circuit

–

DN134 F04

R6

10k

R2

47k

R7

16k

R8

620k

R4

1.6M

R1

33k

R3

10k R5

100k

R10

620k

C4

0.068µF

C3

0.047µF

C5

0.01µF

R13

130k

R12

10k

R15

47k

R14

10k

R24

420

C7

47µF

LOAD UP TO

TEN

PHONES

R23

4.7k

R26

Q5

2N3904

Q4

2N3906

Q2

IRF9620

–180

POWER AMPLIFIER

SMOOTHING FILTER

20Hz OSCILLATORCADENCE OSCILLATOR *

*LED OF OPTO1 ILLUMINATES WHEN THE PHONE IS OFF THE HOOK

R18

100

R17

620

R16

100k

Z1

15V

100k

R25

4.7k

C6

0.033µF

R21

150

R19

620

Z2

15V

R9

300k R11

10k

D1

1N4148

C2

0.47µF

C1

1µF

3

U1B

LT1491 U1C

LT1491

Q1

IRF628 Q3

2N3904

60V

U1D

LT1491

U1A

LT1491

OPTO1

R20

100K

Linear Technology Chronicle •

October 1996

Linear Technology Corporation • 1630 McCarthy Blvd. • Milpitas, California 95035-7417 • (408) 432-1900 • FAX: (408) 434-0507 • For Literature Only: 1-800-4-LINEAR

Linear Technology

Products Are

Distributed By:

Almac/Arrow

Arrow/Schweber

Arrow/Zeus

Digi-Key

Electrosonic

Gerber Electronics

Farnell Electronics

Marshall Industries

Phase 1

Inductorless Switched

Capacitor Converter

Delivers 60mA at 12V

from 5V Source

The LTC1263 is a switched capacitor

charge pump converter which converts a

4.75V to 5.5V input to a regulated 12V out-

put voltage without using inductors. It

delivers up to 60mA of output current at 5V

with 76% efficiency. The LTC1263 typi-

cally draws only 300µA of supply current

while converting, and just 1mA max under

quiescent conditions. A shutdown pin fur-

ther reduces the supply current to less than

1µA, making it suitable for portable and bat-

tery-operated applications. It is ideal for

12V flash memory supplies in PCMCIA

cards, as well as for amplifier or data con-

version supplies in portable, handheld

devices and instruments.

The LTC1263 uses a charge pump tri-

pler, clocked by an internal oscillator, to

LOAD CURRENT (mA)

0 20 40 60 80 100

OUTPUT VOLTAGE (V)

LTC1263 • TA02

13.0

12.8

12.6

12.4

12.2

12.0

11.8

11.6

11.4

11.2

11.0

Figure 1. Output Voltage vs Load

Characteristics for LTC1263

SHDN



OUT



–



+

–



LTC1263

0.47µF

LTC1263 • TA01

10µF

CC

4.75V TO 5.5V

VPP

µP

FLASH

MEMORY

GND

10µF

SHDN

12V

Figure 2. Flash Memory Programming

Supply Using the LTC1263

The LTC1263’s low shutdown current and

lack of a DC current path from input to out-

put are additional battery-saving advantages

over inductor-based micropower boost

switchers.

The LTC1263 is available in an SO-8

package. For a data sheet and evaluation

samples, contact your local Linear

Technology sales office.

generate the 12V output. Figure 1 shows the

output voltage vs load current for a 5V input.

It packs this conversion power into an SO-8

package and requires only four external com-

ponents (see Figure 2), all of which are small

ceramic capacitors (two 0.47µF and two

10µF). Usually an inductor is required to

boost a 5V source to a 12V output with a

current of over 30mA—greatly increasing

the physical size of the DC/DC converter.

Quad C-Load JFET Op

Amps Offer Power

Savings and Picoampere

Inputs

The LT1463 and the LT1465 are quad

JFET input amplifiers that represent an

important addition to LTC’s family of low

power JFETs. These new JFET op amps are

quad versions of the LT1462 and LT1464

duals introduced last month in Linear

Technology Chronicle. The LT1463 has a

slew rate of 0.13V/µs and 175kHz band-

width. The LT1465 has a slew rate of

0.9V/µs and a bandwidth of 1MHz. Figure 1

shows the small-signal response of the

LT1465.

amplifiers offer tremendous power sav-

ings—extending battery life and allowing

more compact designs by running cooler

than other JFETs. They are ideally suited for

battery-powered systems, photo current

amplifiers and as low frequency,

micropower active filters. Figure 2 shows

the LT1465 configured as a Chebyshev

lowpass filter.

The LT1463 and the LT1465 areoffered

in standard 14-pin PDIP and SO packages.

For a data sheet and evaluation samples, get

in touch with your local Linear Technology

sales office.

Figure 2. LT1465 JFET Input Op Amp as a

10MHz 4th Order Chebyshev Lowpass Filter (0.01dB Ripple)

LT1464 • TA05

OUT

TYPICAL OFFSET ≈ 0.6mV

1% TOLERANCES

FOR V

= 10V

P-P

,V

OUT

= –110dB AT f > 300Hz

V

OUT

= –6dB AT f = 16Hz

THE LOW INPUT BIAS CURRENTS ALLOW THE USE OF HIGH RESISTOR VALUES

R3

249k

C2

100nF

C1

33nF

R1

237k

R2

237k

R6

249k

C4

330nF 12

–

1/4 LT1465 14

C3

10nF

R4

154k

R5

154k

15V

–15V

–

1/4 LT1465

5µs/DIV

= 1

= 100pF

1464 G18

50mV/DIV

Figure 1. Small-Signal Response,

VS = ±5V, ±15V, CLOAD = 1000pF

These amplifiers are stable while driv-

ing capacitive loads up to 10nF (10,000pF).

In addition, the input common mode range

includes the positive rail. These quad JFET