AD641 AD [Analog Devices], AD641 Datasheet
AD641
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AD641 Summary of contents
Page 1
... The output current can be converted to a voltage using one of several on-chip resistors to select the slope. A single AD641 provides dynamic range at speeds up to 250 MHz, and two cascaded AD641s together can provide dynamic range at speeds up to 250 MHz. The AD641 is fully stable and well characterized over either the industrial or military temperature ranges ...
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... BW = 100 MHz Pins 5 to Pin 19 Pins 5 to 3/4 0.995 Either Pin to COM Either Pin to COM 4 MIN MAX MIN MAX . IN –2– AD641A AD641S Typ Max Min Typ Max = I LOG |V /V |for 200 mV dc 250 250 +V – 1 –0.3 ...
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... Ambient Temperature Range, Rated Performance Q-20 Industrial, AD641A . . . . . . . . . . . . . . . . . . – +85 C Military, AD641S . . . . . . . . . . . . . . . . . . – +125 C Lead Temperature Range (Soldering 60 sec +300 C *Stresses above those listed under Absolute Maximum Ratings may cause perma- nent damage to the device. This is a stress rating only; functional operation of the ...
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... INPUT VOLTAGE – mV (EITHER SIGN) Figure 7. DC Logarithmic Transfer Function and Error Curve for Single AD641 1.20 1.15 1.10 1.05 1.00 0.95 0.90 0.85 –60 –40 – 100 120 140 TEMPERATURE – C Figure 2. Intercept Voltage vs. X Temperature –60 –40 – 100 120 140 TEMPERATURE – ...
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... Figure 13. Logarithmic Response and Linearity at 200 MHz, T 1.0 0.95 0.90 0.85 0.80 0.75 50 210 230 250 Figure 14. Slope Current, I Figure 15. Baseband Pulse Response of Cascaded AD641s at Inputs of 0.2 mV and 200 mV –5– AD641 +125 C +125 C +25 C +25 C –55 C ERROR –55 C +125 C +25 C +125 C –55 C ...
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... Figure simplified schematic of one stage of the AD641. All transistors in the basic cell operate at near zero collector to base voltage and low bias currents, resulting in low levels of thermally induced distortion ...
Page 7
... Pin 14 when a 2 kHz square-wave input of exactly applied to the AD641. This places the dc intercept at precisely 1 mV. The LOG COM output (Pin 13) is the comple- ment of LOG OUT. It also has intercept, but with an inverted slope of – ...
Page 8
... When using the attenuator, Pin 8 should be grounded, which disables the compensation current. The drift term needs to be compensated only once; when the outputs of two AD641s are summed, Pin 8 should be grounded on at least one of the two devices (both if the attenuator is used). Conversion Range Practical logarithmic converters have an upper and lower limit on the input, beyond which errors increase rapidly ...
Page 9
... AD641s are connected in cascade, most detectors will be adequately loaded due to the high overall gain, but a single AD641 does not have sufficient gain to maintain high accuracy for low level sine wave or triwave inputs. Figure 23 shows the absolute deviation from calibration for the same three waveforms for a single AD641. For inputs between – ...
Page 10
... V per decade. Use of the LOG COM output in this way provides a numerically correct decibel read- ing on a DVM (+100 mV = +1.00 dB). Board layout is very important. The AD641 has both high gain and wide bandwidth; therefore every signal path must be very carefully considered. A high quality ground plane is essential, ...
Page 11
... Pin 1. The residual offset is then due to the bias current offset, which is typically under 1 A, causing an extra offset uncertainty of 100 V in this example. For a single AD641 this will rarely be troublesome, but in some applications it may need to be nulled out, along with the internal voltage offset component. This may be achieved by adding an adjustable voltage 250 V at the unused input ...
Page 12
... It may occasionally be desirable to attenuate the signal even further. For example, the source may have a full-scale value and since the basic range of the AD641 extends only to 200 mV dc, an attenuation factor of 50 might be chosen. This may be achieved either by using an independent external ...
Page 13
... OPERATION OF CASCADED AD641S Frequently, the dynamic range of the input will more. Two AD641s can be cascaded, as shown in Figure 27. The balanced signal output from U1 becomes the input to U2. Resistors are included in series with each LOG OUT pin and capacitors C1 and C2 are placed directly between Pins 13 and 14 to provide a local path for the RF current at these output pairs ...
Page 14
... RSSI application this signal that is monitored to determine where to stop during seek or scan operations. The AD641 is used to measure the strength of the incoming RF signal and outputs a current that is proportional to the loga- rithm of its ac amplitude. In this manner signal amplitudes with a wide dynamic range and wide bandwidth can be measured ...
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... MHz RSSI Converter with 58 dB Dynamic Range For a larger dynamic range two AD641s can be cascaded, as shown in Figure 32. The low end usefulness of the circuit will be set by the noise floor of the overall environment that the circuit sees ...
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... AD641 20-Lead Plastic DIP (N-20) 1.060 (26.90) 0.925 (23.50 0.280 (7.11) 0.240 (6.10 PIN 1 0.060 (1.52) 0.015 (0.38) 0.210 (5.33) MAX 0.130 (3.30) 0.160 (4.06) MIN 0.115 (2.93) 0.100 SEATING 0.022 (0.558) 0.070 (1.77) PLANE (2.54) 0.014 (0.356) 0.045 (1.15) BSC 0.048 (1.21) 0.042 (1.07) OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 0.005 (0.13) MIN PIN 1 0.325 (8.25) ...