5962-89807012A 데이터 시트보기 (PDF) - Analog Devices

부품명

상세내역

제조사

5962-89807012A

Balanced Modulator/Demodulator

Analog Devices 

AD630

BALANCED DEMODULATOR

The balanced modulator topology described above will also act as

a balanced demodulator if a double sideband suppressed carrier

waveform is applied to the signal input and the carrier signal is

applied to the reference input. The output under these circumstances

will be the baseband modulation signal. Higher order carrier

components that can be removed with a low-pass filter will

also be present. Other names for this function are synchro-

nous demodulation and phase-sensitive detection.

PRECISION PHASE COMPARATOR

The balanced modulator topologies of Figures 9a and 9b can

also be used as precision phase comparators. In this case, an ac

waveform of a particular frequency is applied to the signal input

and a waveform of the same frequency is applied to the refer-

ence input. The dc level of the output (obtained by low-pass

filtering) will be proportional to the signal amplitude and phase

difference between the input signals. If the signal amplitude is

held constant, the output can be used as a direct indication of

the phase. When these input signals are 90° out of phase, they

are said to be in quadrature and the AD630 dc output will be zero.

PRECISION RECTIFIER ABSOLUTE VALUE

If the input signal is used as its own reference in the balanced

modulator topologies, the AD630 will act as a precision recti-

fier. The high frequency performance will be superior to that

which can be achieved with diode feedback and op amps. There

are no diode drops that the op amp must “leap over” with the

commutating amplifier.

LVDT SIGNAL CONDITIONER

Many transducers function by modulating an ac carrier. A linear

variable differential transformer (LVDT) is a transducer of

this type. The amplitude of the output signal corresponds to

core displacement. Figure 11 shows an accurate synchronous

demodulation system which can be used to produce a dc voltage

that corresponds to the LVDT core position. The inherent

precision and temperature stability of the AD630 reduce

demodulator drift to a second-order effect.

E1000

SCHAEVITZ AD544

A LVDT FOLLOWER

16 B 5k⍀

AD630

؎2 DEMODULATOR

15

1 2.5k⍀

10k⍀

2.5kHZ

2V p-p

SINUSOIDAL

EXCITATION

20 A

14 10k⍀ 19

17

B

C 13 100k⍀ D

12

1␮F

2.5k⍀

PHASE

9

SHIFTER

10

Figure 11. LVDT Signal Conditioner

AC BRIDGE

Bridge circuits that use dc excitation are often plagued by

errors caused by thermocouple effects, 1/f noise, dc drifts in the

electronics, and line noise pick-up. One way to get around these

problems is to excite the bridge with an ac waveform, amplify the

bridge output with an ac amplifier, and synchronously demodulate

the resulting signal. The ac phase and amplitude information

from the bridge is recovered as a dc signal at the output of the

synchronous demodulator. The low frequency system noise,

dc drifts, and demodulator noise all get mixed to the carrier

frequency and can be removed by means of a low-pass filter.

Dynamic response of the bridge must be traded off against the

amount of attenuation required to adequately suppress these

residual carrier components in the selection of the filter.

Figure 12 is an example of an ac bridge system with the AD630

used as a synchronous demodulator. The bridge is excited by a

1 V 400 Hz excitation. Trace A in Figure 13 is the amplified

bridge signal. Trace B is the output of the synchronous demodu-

lator and Trace C is the filtered dc system output.

1V

400Hz

350⍀

350⍀

+15V

350⍀

+IN

350⍀

49.9⍀

A

AD8221

REF

–IN

9

11

SEL B

+VS

16 RA

17 RINB

19 CH B–

20 CH A–

AD630AR

B

VOUT 13

COMP 12

4.99k⍀

2␮F

15 RF RINA SEL A –VS RB

1

10

8 14

4.99k⍀

2␮F

C

4.99k⍀

2␮F

–15V

Figure 12. AC Bridge System

REV. E

–9–

Share Link: