AD8304 Analog Devices, AD8304 Datasheet
AD8304
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AD8304 Summary of contents
Page 1
... V reference, for example, in alarm applications. The incremental bandwidth of a translinear logarithmic amplifier inherently diminishes for small input currents. At the 1 nA level, the AD8304’s bandwidth is about 2 kHz, but this increases in proportion to I mum value of 10 MHz. ...
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... AD8304–SPECIFICATIONS Parameters Conditions INPUT INTERFACE Pin 4, INPT; Pin 3 and Pin 5, VSUM Specified Current Range Flows toward INPT pin Input Node Voltage Internally preset; May Be Altered Temperature Drift –40°C < T Input Guard Offset Voltage PHOTODIODE BIAS Established between Pin 6, V ...
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... ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the AD8304 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high-energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality ...
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... AD8304–Typical Performance Characteristics ( unless otherwise noted 1 –40 C, + –0.5V 1.4 N –40 C 1.2 +25 C +85 C 1.0 0.8 0.6 0.4 0.2 0 100p 1n 10n 100n 1 INPUT – –40 C, + –0.5V 1.5 N 1.0 –40 C 0.5 + +85 C –0.5 –1.0 –1.5 –2.0 ...
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... GAIN = 2 –3 –6 –9 –12 100 1m 10m 1kHz C 0 –10 –20 –30 –40 –50 –60 – 10M AD8304 100n 1 10 100 1m 10m INPUT CURRENT – 2 10k 100k 1M 10M 100M FREQUENCY – Hz ...
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... AD8304 2 1.5 1.0 0.5 MEAN + 3 0 MEAN – 3 –0.5 –1.0 –1.5 –2.0 100p 1n 10n 100n 1 10 INPUT – A σ MEAN + MEAN –1 MEAN – –2 –3 –4 –5 100p 1n 10n 100n 1 10 INPUT – ...
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... LOGARITHMIC SLOPE – mV/dec 160 140 120 100 180 160 140 120 100 204 –20 AD8304 80 100 120 140 LOGARITHMIC INTERCEPT – pA – INPUT GUARD OFFSET – mV ...
Page 8
... For the AD8304 operating in its default mode, its I corresponds responsivity of 0.9 A/W. Thus, an optical power would generate: V LOG Note that when using the AD8304 in optical applications, the (2) interpretation of V power, the logarithmic slope remains 10 mV/dB at this output. This can be a little confusing since a decibel change on the is called Z optical side has a different meaning than on the electrical side ...
Page 9
... VREF. In conventional translinear log amps, the summing node is gener- ally held at ground potential, but that condition is not readily realized in a single-supply part. To address this, the AD8304 also supports the use of an optional negative supply voltage, V pin VNEG. For least –0.5 V the summing node can N be connected to ground potential ...
Page 10
... R1 Figure 1, which is necessary to stabilize the system over the full range of currents, affects bandwidth at all values of I Later signal processing blocks also limit the maximum value. TPC 7 shows ac response curves for the AD8304 at eight repre- sentative currents of 100 mA, using 1000 pF ...
Page 11
... Table III lists the resistor values for 0.5V representative intercepts. RZ VLOG 8 5k BFIN BFNG 13 (mV/decade) 300 RA RB 300 11 400 VOUT V 400 OUT 400 500 500 500 Equations for use with Table III: V OUT where = + G AD8304 (pA 20.0 100 10 10.0 100 50 3.01 100 1 10.0 12.4 10 8.06 12.4 50 6.65 12.4 1 11.5 8.2 10 9.76 8 ...
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... VREF VREF 7 particular diode, limited mainly by its series resistance. To address 0.5V this matter, the AD8304 provides for the diode a bias that varies linearly with the current. This voltage appears at pin VPDB, and VLOG 8 varies from 0.6 V (reverse-biasing the diode by 0.1 V) for RC ...
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... 1nF 10nF R1 750 CONNECT Using a Negative Supply Most applications of the AD8304 will require only a single supply 3 5.5 V. However, to provide further versatility, dual supplies may be employed, as illustrated in Figure 10. 12 The use of a negative supply, V VREF VREF 7 be placed exactly at ground level, because the input transistor (Q1 in Figure 1) will have a negative bias on its emitter small as – ...
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... RB and RE) at high input cur- rents. Therefore advisable to set these to zero. While this will not model the AD8304 precisely safer than using pos- sibly high default values for these parameters. The low current model parameters may also need consideration. Note that no attempt is made to capture either dynamic behavior or the effects of temperature in this simple macromodel ...
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... The minimum voltage that can be accurately measured is then limited only by the drift in the input offset of the AD8304. The specifications show the maximum spread over the full tempera- ture and supply range. Over a limited temperature range, and with a regulated supply, the offset drift will be lower; in this situa- tion, processing of inputs down practicable ...
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... AD8304 Programmable Multidecade Current Source The AD8304 supports a wide variety of general (nonoptical) applications. For example, the need frequently arises in test equipment to provide an accurate current that can be varied over many decades. This can be achieved using logarithmic amplifier as the measuring device in an inverse function loop, as illustrated in Figure 16 ...
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... Characterization Setups and Methods During the primary characterization of the AD8304, the device was treated as a high precision current-in logarithmic amplifier (converter). Rather than attempting to accurately generate photocurrents by illuminating a photodiode, precision current sources, like the Keithley 236, were used as input sources. Great care was taken when applying the low-level input currents ...
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... AD8304 Evaluation Board An evaluation board is available for the AD8304, the schematic for which is shown in Figure 21, and the two board sides are shown in Figure 22 and Figure 23. It can be configured for a wide variety of experiments. The board is factory set for photoconductive mode R10 10k ...
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... N SW1, R10 Device Enable: When SW1 is in the “0” position, the PWDN pin is connected to ground and the AD8304 is in its normal operating mode. R1, R2 Buffer Amplifier Gain/Slope Adjustment: The logarithmic slope of the AD8304 can be altered using the buffer’s gain-setting resistors, R1 and R2 ...
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... AD8304 SEATING OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 14-Lead TSSOP (RU-14) 0.201 (5.10) 0.193 (4.90 0.177 (4.50) 0.169 (4.30) 0.256 (6.50) 0.246 (6.25 PIN 1 0.006 (0.15) 0.0433 (1.10) MAX 0.002 (0.05) 8 0.0256 0.0118 (0.30) 0 0.0079 (0.20) (0.65) 0.0075 (0.19) PLANE 0.0035 (0.090) BSC 0.028 (0.70) 0.020 (0.50) ...