LT2178 datasheet(16/28 Pages) LINER

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LTC6258/LTC6259/LTC6260

6258960fa

For more information www.linear.com/LTC6258

Figure 4b. Low Power Sine Generator

Figure 4c. FFT

Figure 4a. Low Power Squarewave - Sinewave Oscillator

APPLICATIONS INFORMATION

Low Power Sine Wave Generator

Alowpowersinewavegeneratorcanbederivedbydrivinga

squarewaveintothebandpassfilter.Acompleteschematic

is shown in Figure 4a. The LTC6992-1 easily configures

as a 50% duty cycle 10kHz square wave, and can drive

the relatively benign loading seen in the bandpass filter.

Figures4band4cshowtheLTC6992-1outputandbandpass

filter output. THD of the sine wave is –30.5 dBc. Note, even

harmonics that appear in the distortion products of the

filtered output already appear in the source square wave.

Low Noise Reference

The LT6656 is a 1µA precision series voltage reference.

Yet with low power comes low drive current capability

and higher noise. The LTC6259 can be used as a buf-

fer that follows a filter to enhance the utilization of the

LT6656 in low power applications. Figure 5a shows such

a configuration. First a very low cutoff frequency follows

the LT6656 output (RIN1 and CIN1, lower than 5Hz cutoff).

Choice of filter resistor RIN1 is such that the bias current in

the LTC6259, multiplied by the resistance value, is lower

than the nominal offset voltage of the op amp. CIN1 can

be larger or smaller, with more or less filtering accord-

ingly. The voltage withstanding requirement of CIN1 is low,

resulting in large capacitance in a small volume.

V+

4.7nF

21k

4.7nF

154k

182k

976k

0.1µF

154k

562

499k

6258 F04a

499k

1µF

10k

MOD

LTC6992-1

GND

SET

OUT

V+

DIV

OUT

0.1µF

LT6258

–

V+

50µs/Div

1.0

2.0

3.0

4.0

5.0

6258 F04b

FILTERED OUTPUT

SQUARE WAVE

FREQUENCY (kHz)

0 10 20 30 40 50 60 70 80 90 100

–120

–100

–80

–60

–40

–20

6258 F04c

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