Analog Devices AD602, AD600 manual RMS Responding AGC Circuit with 100 dB Dynamic Range

Page 14

AD600/AD602

INPUT

1V RMS

MAX

(SINE WAVE)

C1LO

A1HI

A1LO

GAT1

GAT2

A2LO

A2HI C2LO

R13

3.01kΩ

1

 

16

C1HI

 

 

 

 

 

 

 

 

 

C1LO

1

16

C1HI

 

 

 

 

 

 

 

 

 

R3

 

 

 

2

 

15

A1CM

 

 

 

 

R2

 

 

 

A1HI

2

15

A1CM

 

C1

 

 

 

 

200Ω

 

 

 

 

 

487Ω

 

 

 

 

A1

 

A1OP

 

U3A

 

 

 

A1LO

 

A1

A1OP

 

 

 

 

 

 

 

 

 

 

3

 

14

0.1 F

 

 

 

 

 

 

 

 

3

14

4

 

13

VPOS

+5V DEC

 

1/4

 

 

 

 

 

 

GAT1

4

13

VPOS

 

 

 

 

 

 

 

 

 

 

+5V DEC

 

REF

 

VNEG

R1

 

AD713

 

 

 

 

 

GAT2

 

REF

VNEG

5

12

–5V DEC 133kΩ

 

 

 

 

 

 

5

 

 

 

C2

 

 

 

 

 

 

 

12

–5V DEC

 

 

 

A2OP

 

 

R5

 

 

 

 

 

A2LO

 

 

 

6

 

11

 

 

0.1F

 

 

 

 

 

6

11

A2OP

 

 

 

 

1.58kΩ

 

 

 

 

 

 

 

A2

 

 

 

 

 

 

 

 

 

 

 

 

A2

 

 

 

A2CM

 

 

 

 

 

 

 

 

 

A2HI

 

A2CM

7

 

10

 

 

 

 

 

 

 

 

 

7

10

 

 

 

 

 

 

 

 

 

U3B

 

 

 

 

 

 

C2HI

 

 

R4

C3

 

 

 

 

C2LO

 

 

C2HI

8

 

9

 

 

 

 

 

 

 

8

9

 

 

 

133kΩ

220pF

 

 

 

1/4

 

 

 

U1 AD600

 

 

 

 

 

 

 

 

 

U2 AD600

 

 

 

 

 

 

 

 

 

 

AD713

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

+5V

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

–2dB

 

 

+2dB

 

 

 

FB

 

 

 

 

 

 

 

–62.5mV

0dB

+62.5mV

 

 

 

 

0.1F

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

–5V

 

 

 

 

 

+5V

 

 

 

+5V DEC

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

R6

 

 

R7

 

R8

R9

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

10kΩ

 

127Ω

127Ω

10kΩ

 

 

 

–5V DEC

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FB

 

0.1F

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

C5

 

 

 

 

 

 

 

 

 

 

–5V

 

 

 

 

 

22F

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

+5V DEC

 

 

 

POWER SUPPLY

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DECOUPLING NETWORK

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1

VINP

VPOS

14

 

 

 

 

 

 

 

 

 

 

+5V DEC

NC

2

 

U4

13

 

NC

 

 

 

 

 

 

 

 

 

 

AD636

 

 

 

R11

 

 

 

 

 

 

R15

 

 

 

 

 

 

 

 

 

 

 

 

 

–5V DEC

3

VNEG

 

12

 

NC

 

 

46.4kΩ

 

 

 

 

 

 

19.6kΩ

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

C6

 

 

 

 

 

 

 

 

4

CAVG

11

 

NC

R10

 

 

 

 

 

 

 

 

 

4.7F

 

 

 

 

 

 

 

 

 

3.16kΩ

 

 

 

 

 

 

R16

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NC

5

VLOG

COMM

10

 

 

 

 

 

 

 

 

Q1

 

 

6.65kΩ

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2N3906

R14

 

 

NC

6

BFOP

LDLO

9

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

301kΩ

 

 

7

 

 

8

 

 

 

 

U3C

 

VLOG

 

 

 

 

 

 

BFIN

VRMS

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1/4

 

 

 

R12

 

 

 

 

 

 

 

 

 

 

+316.2mV

AD713

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

11.3kΩ

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NC = NO CONNECT

C4

2F VOUT

Figure 25. RMS Responding AGC Circuit with 100 dB Dynamic Range

100 dB to 120 dB RMS Responding Constant Bandwidth AGC Systems with High Accuracy dB Outputs

The next two applications double as both AGC amplifiers and measurement systems. In both, precise gain offsets are used to achieve either (1) a very high gain linearity of ± 0.1 dB over the full 100 dB range, or (2) the optimal signal-to-noise ratio at any gain.

A 100 dB RMS/AGC System with Minimal Gain Error (Parallel Gain with Offset)

Figure 25 shows an rms-responding AGC circuit, which can equally well be used as an accurate measurement system. It accepts inputs of 10 μV to 1 V rms (–100 dBV to 0 dBV) with generous overrange. Figure 26 shows the logarithmic output, VLOG, which is accurately scaled 1 V per decade, that is,

50 mV/dB, with an intercept (VLOG = 0) at 3.16 mV rms

(–50 dBV). Gain offsets of ± 2 dB have been introduced between the amplifiers, provided by the ± 62.5 mV introduced by R6–R9. These offsets cancel a small gain ripple which arises in the X-AMP from its finite interpolation error, which has a period of 18 dB in the individual VCA sections. The gain ripple of all three amplifier sections without this offset (in which case the gain errors simply add) is shown in Figure 27; it is still a

remarkably low ± 0.25 dB over the 108 dB range from 6 μV to

1.5V rms. However, with the gain offsets connected, the gain linearity remains under ± 0.1 dB over the specified 100 dB range (Figure 28).

 

5

 

 

 

 

 

 

 

 

 

 

 

Volts–

4

 

 

 

 

 

2

 

 

 

 

 

 

3

 

 

 

 

 

OUTPUT

1

 

 

 

 

 

 

 

 

 

 

 

LOGARITHMIC

0

 

 

 

 

 

–3

 

 

 

 

 

 

–1

 

 

 

 

 

 

–2

 

 

 

 

 

 

–4

 

 

 

 

 

 

–5

 

 

 

 

 

 

 

 

 

 

 

 

1V

10V 100V 1mV 10mV 100mV

1V

10V

INPUT SIGNAL – V RMS

Figure 26. VLOG Plotted vs. VIN for Figure 25‘s Circuit Showing 120 dB AGC Range

–14–

REV. A

Image 14
Contents Functional Block Diagram Product DescriptionREV. a Ordering Guide Connection DiagramAbsolute Maximum RATINGS1 PIN DescriptionTheory of Operation Noise PerformanceGain-Control Interface Signal-Gating InputsSequential Mode Maximum S/N Ratio Common-Mode RejectionLow Ripple Mode Minimum Gain Error Where VC is the applied control voltageParallel Mode Simplest Gain-Control Interface AD600/AD602 Applications Low Noise AGC Amplifier with 80 dB Gain Range Low Noise, 6 dB PreamplifierTable I. Measured Preamplifier Performance AD600/AD602 AD600/AD602 U1 AD600 DB Output of ’s Circuit Is Linear Over an 80 dB Range RMS Responding AGC Circuit with 100 dB Dynamic Range Gain Error for Without the 2 dB Offset Modification DB RMS/AGC System with Optimal S/N Ratio Sequential Gain0dB Adjust AD600/AD602 AD600/AD602-Typical Performance Characteristics Gating Feedthrough to Output, Gating Off to On Pin Soic R-16 Package Outline DimensionsPin Plastic DIP N-16 Package Pin Cerdip Q-16 Package

AD600, AD602 specifications

Analog Devices, a leader in high-performance signal processing, offers the AD602 and AD600, two versatile RF amplifiers known for their impressive performance in a variety of applications. The AD602 is a dual-channel, low-noise variable gain amplifier (VGA), while the AD600 is a similar VGA but designed for single-channel applications. Both devices are highly regarded in the fields of communications, instrumentation, and imaging, as they provide outstanding performance in amplifying weak signals.

The AD602 features a gain range of -6 dB to +40 dB, allowing for precise control of the output signal strength. This flexibility makes it well-suited for applications such as IF amplification, where signal levels can vary significantly. The device also includes a low distortion characteristic, enabling it to maintain signal integrity even when handling larger input signals. With a wide bandwidth spanning from DC to 100 MHz, the AD602 caters to applications requiring both low-frequency and high-frequency performance.

On the other hand, the AD600 shares many similarities with the AD602 but offers slightly different characteristics. With a gain range of -1.5 dB to +40 dB, it offers a broader range of control for its output signal strength. Like the AD602, its low distortion and high linearity are crucial for high-fidelity signal processing. The AD600 is also capable of delivering a high output current, making it favorable for driving capacitive loads effectively.

Both devices employ Analog Devices' proprietary topology that minimizes the effects of thermal drift and achieves high levels of performance under varying conditions. They are built with advanced manufacturing processes that ensure stability and reliability in industrial applications. Integrated with differential inputs, these devices help eliminate common-mode noise, thus improving overall signal quality.

The AD602 and AD600 are equipped with comprehensive protection features, enabling them to withstand overload conditions without compromising performance. Their low noise figure contributes to excellent low-level signal recovery, making these amplifiers ideal for radar receivers, medical imaging systems, and satellite communication.

In summary, the AD602 and AD600 by Analog Devices stand out as powerful, reliable variable gain amplifiers with robust performance characteristics. Their flexibility in gain control, low distortion, high linearity, and advanced protection features make them invaluable components in modern electronic systems, enhancing the quality and reliability of signal processing applications across various industries.