Datasheet

Data Sheet AD636
Rev. E | Page 13 of 16
Frequency Response ±3 dBm
Input
0 dBm = 5 Hz to 380 kHz
−10 dBm = 5 Hz to 370 kHz
−20 dBm = 5 Hz to 240 kHz
−30 dBm = 5 Hz to 100 kHz
−40 dBm = 5 Hz to 45 kHz
−50 dBm = 5 Hz to 17 kHz
Calibration
First, calibrate the 0 dB reference level by applying a 1 kHz sine
wave from an audio oscillator at the desired 0 dB amplitude.
This can be anywhere from 0 dBm (770 mV rms − 2.2 V p-p)
to −20 dBm (77 mV rms − 220 mV p-p). Adjust the I
REF
calibration trimmer for a zero indication on the analog meter.
Then, calibrate the meter scale factor or gain. Apply an input
signal −40 dB below the set 0 dB reference and adjust the scale
factor calibration trimmer for a 40 μA reading on the analog meter.
The temperature compensation resistors for this circuit can be
purchased from Micro-Ohm Corporation, 1088 Hamilton Rd.,
Duarte, CA 91010, Part #Type 401F, 2 kΩ ,1% + 3500 ppm/°C.
R2
900kΩ
1
2
3
4
5
6
7
AD636
14
13
12
11
10
9
8
BUF
+
–
+
–
+
+
–
+V
DD
REF HI
REF LO
COM
HI
LO
+
–
+
ON
OFF
LXD 7543
LIN
dB
LIN
dB
LIN
dB
200mV
2V
20V
200V
COM
V
IN
R1
9MΩ
R3
90kΩ
R4
10kΩ
C3
0.02µF
R5
47kΩ
1W
10%
D1
1N4148
C4
2.2µF
R6
1MΩ
ABSOLUTE
VALUE
SQUARER
DIVIDER
CURRENT
MIRROR
6.8µF
R7
20kΩ
D4
1N4148
10kΩ
10kΩ
C7
6.8µF
D2
1N4148
R8
2.49kΩ
+V
S
R9
100kΩ
0dB SET
R10
20kΩ
D3
1.2V
AD589
LIN
SCALE
R15
1MΩ
C6
0.01µF
–V
S
–V
SS
ANALOG
IN
3-1/2 DIGIT
7106 TYPE
A/D
CONVERTER
+V
DD
–V
SS
9V
BATTERY
1µF
R11
10kΩ
R12
1kΩ
R13
500Ω
R14
10kΩ
dB
SCALE
3-1/2
DIGIT
LCD
DISPLAY
00787-018
V
IN
NC
–V
S
C
AV
dB
BUF OUT
BUF IN
+V
S
NC
NC
NC
COM
R
L
I
OUT
NC = NO CONNECT
Figure 17. Portable, High-Z Input, RMS DPM and dB Meter Circuit
ALL RESISTORS 1/4W 1% METAL FILM UNLESS OTHERWISE STATED EXCEPT
*WHICH IS 2kΩ +3500ppm 1% TC RESISTOR.
1
2
3
4
5
6
7
AD636
14
13
12
11
10
9
8
BUF
+
–
+ –
+
–
µA776
+ –
+
+
+
+
ON/OFF
9V
+1.2V
AD589J
250µA
100µA
+
+4.2V
–4.8V
D1
1N6263
SIGNAL
INPUT
C4
0.1µF
R8
47kΩ
1W
D2
1N6263
C1
3.3µF
R1
1MΩ
C2
6.8µF
10kΩ
10kΩ
R9
10kΩ
ABSOLUTE
VALUE
SQUARER
DIVIDER
CURRENT
MIRROR
R2
12.7kΩ
C3
10µF
C5
10µF
R10
20kΩ
C6
0.1µF
*R7
2kΩ
R6
100Ω
R3
5kΩ
R4
500kΩ
I
REF
ADJUST
R11
820kΩ
5%
0–50µA
R5
10kΩ
SCALE FACTOR
ADJUST
2
3
4
8
7
6
00787-019
NC = NO CONNECT
V
IN
NC
–V
S
C
AV
dB
BUF OUT
BUF IN
+V
S
NC
NC
NC
COM
R
L
I
OUT
Figure 18. Low Power, High Input Impedance dB Meter