AD600/AD602

REV. A

–16–

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

REF

A1

A2

C1HI

A1CM

A1OP

VPOS

VNEG

A2OP

A2CM

C2HI

C1LO

A1HI

A1LO

GAT1

GAT2

A2LO

A2HI

C2LO

U1 AD600

+6V DEC

–6V DEC

U3A

1/4

AD713

R2

100

Ω

C1

0.1

µF

U3B

1/4

AD713

R1

133k

Ω

C2

0.1

µF

R5

5.36k

Ω

R4

133k

Ω

C3

0.001

µF

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

REF

A1

A2

C1HI

A1CM

A1OP

VPOS

VNEG

A2OP

A2CM

C2HI

C1LO

A1HI

A1LO

GAT1

GAT2

A2LO

A2HI

C2LO

U2 AD600

+6V DEC

–6V DEC

C4

2

µF

C5

22

µF

1

2

3

4

5

6

7

14

13

12

11

10

9

8

NC

NC

NC

–6V DEC

U3C

R11

56.2k

Ω

+6V DEC

NC

NC

NC

1/4

AD713

+316.2mV

VINP

VNEG

CAVG

VLOG

BFOP

BFIN

VPOS

COMM

LDLO

V

U4

AD636

NC = NO CONNECT

0.1

µF

0.1

µF

FB

–6V

+6V

POWER SUPPLY

DECOUPLING NETWORK

+6V DEC

–6V DEC

FB

R10

3.16k

Ω

C6

4.7

µF

R15

5.11k

Ω

R14

7.32k

Ω

+6V DEC

R13

866

Ω

R12

1k

Ω

INPUT

R17

115

Ω

R3

200

Ω

R6

3.4k

Ω

+6V

R7

1k

Ω

R8

294

Ω

R9

1k

Ω

R16

287

Ω

RMS

Figure 29. 120 dB Dynamic Range RMS Responding Circuit Optimized for S/N Ratio

resistance of U1A as well as the fixed 6 dB attenuation provided

by R2 and the input resistance of U1B are included both to set

100 dB range between 10

µV rms and 1 V rms input. R5 and

C3 provide a 3 dB noise bandwidth of 30 kHz. R12 to R15

change the scaling from 625 mV/decade at the control inputs to

1 V/decade at the output and at the same time center the dy-

within the

±6 V supplies.

Figure 31 shows the error ripple due to the individual gain func-

tions which is bounded by

±0.2 dB (dotted lines) from 6 µV to

2 V. The small perturbations at about 200

µV and 20 mV,

caused by the impracticality of matching the gain functions per-

fectly, are the only sign that the gains are now sequential. Fig-

of 316 mV rms over the full 120 dB range.

To more directly compare the signal-to-noise ratios in the

“simultaneous” and “sequential” modes of operation, all inter-

stage attenuation was eliminated (R2 and R3 in Figure 25, R2 in

Figure 29), the input of U1A was shorted, R5 was selected to

provide a 20 kHz bandwidth (R5 = 7.87 k

Ω), and only the gain

control was varied, using an external source. The rms value of

5

3

–5

1

µV10µV

10V

1V

100mV

10mV

1mV

100

µV

4

2

0

1

–1

–3

–2

–4

INPUT SIGNAL – V RMS

Range

ratio relative to 0 dBV, this being almost the maximum output

capability of the AD600. Results for the simultaneous mode can

be seen in Figure 33. The S/ N ratio degreades uniformly as the

gain is increased. Note that since the inverting gain control was

used, the gain in this curve and in Figure 34 decreases for more

positive values of the gain-control voltage.