LTC6244HVCMS8 datasheet(20/24 Pages) LINER

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LTC6244

6244f

A Low Noise AC Difference Ampliﬁer

In the signal conditioning of wideband sensors and trans-

ducers, a low noise ampliﬁer is often used to provide gain

for low level AC difference signals in the frequency range

of a few Hertz to hundreds of kilo-Hertz. In addition, the

ampliﬁer must reject common mode AC signals and its input

impedance should be higher than the differential source

impedance. Typical applications are piezoelectric sensors

used in sonar, sound and ultrasound systems and LVDT

(linear variable differential transformers) for displacement

measurements in process control and robotics.

The Figure 11a circuit is a low noise, single supply AC

difference ampliﬁer. The ampliﬁer’s low frequency –3dB

bandwidth is set with resistor R5 and capacitor C3, while

the upper –3dB bandwidth is set with R2 and C1. The

input common mode DC voltage can vary from ground to

V+ and the output DC voltage is equal to the VREF voltage.

The ampliﬁer’s gain is the ratio of resistors R2 to R1 (R4

= R2 and R3 = R1). The component values in the circuit

of Figure 11a implement an 800Hz to 160kHz AC ampli-

ﬁer with a gain equal to 10 and 12nV/√Hz input referred

voltage noise density shown in Figure 11b. The total input

referred wideband noise is 4.5µVRMS, in the bandwidth

of 500Hz to 200kHz.

APPLICATIO S I FOR ATIO

Input Impedance = 2 • RIN

Gain

OUT

+ –

–

NIN

Maximum

–

Gain =

5MHz

f3dB

439

8 977

••

.•

•

fGain

Gain

Gain R

()

4000

••

•

Figure 9b. Design Equations for Figure 9a Circuit

10k

100k

FREQUENCY (Hz)

6244 F10

f–3dB = 970kHz

GAIN = 5

RIN = 4k

Figure 10. Differential Input Referred Noise

VIN

10k

RIN

CIN

82pF

CIN

82pF

33pF

–

1/2

LTC6244

VOUT

–

1/2

LTC6244

VOUT

–

6244 F09a

V+

V–

10k

VIN

–

Figure 9a. Low Noise Fully Differential Buffer/Ampliﬁer

(f–3dB = 970kHz, Gain = 5, RIN = 4k)

LTC6244HVCMS8 Datasheet(PDF) 20 Page - Linear Technology

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