Zakładka z wyszukiwarką danych komponentów |
|
AD636J Arkusz danych(PDF) 7 Page - Analog Devices |
|
AD636J Arkusz danych(HTML) 7 Page - Analog Devices |
7 / 8 page AD636 REV. B –7– Circuit Description The input voltage, VIN, is ac coupled by C4 while resistor R8, together with diodes D1, and D2, provide high input voltage protection. The buffer’s output, Pin 6, is ac coupled to the rms converter’s input (Pin 1) by capacitor C2. Resistor, R9, is connected between the buffer’s output, a Class A output stage, and the negative output swing. Resistor R1, is the amplifier’s “bootstrapping” resistor. With this circuit, single supply operation is made possible by setting “ground” at a point between the positive and negative sides of the battery. This is accomplished by sending 250 µA from the positive battery terminal through resistor R2, then through the 1.2 volt AD589 bandgap reference, and finally back to the negative side of the battery via resistor R10. This sets ground at 1.2 volts +3.18 volts (250 µA × 12.7 kΩ) = 4.4 volts below the positive battery terminal and 5.0 volts (250 µA × 20 kΩ) above the negative battery terminal. Bypass capacitors C3 and C5 keep both sides of the battery at a low ac impedance to ground. The AD589 bandgap reference establishes the 1.2 volt regulated reference voltage which together with resistor R3 and trimming potentiometer R4 set the zero dB reference current IREF. Performance Data 0 dB Reference Range = 0 dBm (770 mV) to –20 dBm (77 mV) rms 0 dBm = 1 milliwatt in 600 Ω Input Range (at IREF = 770 mV) = 50 dBm Input Impedance = approximately 1010 Ω VSUPPLY Operating Range +5 V dc to +20 V dc IQUIESCENT = 1. 8 mA typical Accuracy with 1 kHz sine wave and 9 volt dc supply: 0 dB to –40 dBm ± 0.1 dBm 0 dBm to –50 dBm ± 0.15 dBm +10 dBm to –50 dBm ± 0.5 dBm 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 1. First calibrate the zero dB reference level by applying a 1 kHz sine wave from an audio oscillator at the desired zero dB amplitude. This may be anywhere from zero dBm (770 mV rms – 2.2 volts p-p) to –20 dBm (77 mV rms 220 mV – p-p). Adjust the IREF cal trimmer for a zero indication on the analog meter. 2. The final step is to calibrate the meter scale factor or gain. Apply an input signal –40 dB below the set zero 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 may be purchased from: Tel Labs Inc., 154 Harvey Road, P.O. Box 375, Londonderry, NH 03053, Part #Q332A 2 k Ω 1% +3500 ppm/°C or from Precision Resistor Company, 109 U.S. Highway 22, Hill- side, NJ 07205, Part #PT146 2 k Ω 1% +3500 ppm/°C. resemble low duty cycle pulse trains, such as those occurring in switching power supplies and SCR circuits, have high crest factors. For example, a rectangular pulse train with a 1% duty cycle has a crest factor of 10 (C.F. = 1 η ). Figure 13 is a curve of reading error for the AD636 for a 200 mV rms input signal with crest factors from 1 to 7. A rectangular pulse train (pulse width 200 µs) was used for this test since it is the worst-case waveform for rms measurement (all the energy is contained in the peaks). The duty cycle and peak amplitude were varied to produce crest factors from 1 to 7 while maintain- ing a constant 200 mV rms input amplitude. CREST FACTOR 0.5 0 –1.0 17 2 3456 –0.5 T VP 0 200 s EO = DUTY CYCLE = CF = 1/ EIN (rms) = 200mV 200 s T Figure 13. Error vs. Crest Factor A COMPLETE AC DIGITAL VOLTMETER Figure 14 shows a design for a complete low power ac digital voltmeter circuit based on the AD636. The 10 M Ω input attenuator allows full-scale ranges of 200 mV, 2 V, 20 V and 200 V rms. Signals are capacitively coupled to the AD636 buffer amplifier, which is connected in an ac bootstrapped configura- tion to minimize loading. The buffer then drives the 6.7 k Ω input impedance of the AD636. The COM terminal of the ADC chip provides the false ground required by the AD636 for single supply operation. An AD589 1.2 volt reference diode is used to provide a stable 100 millivolt reference for the ADC in the lin- ear rms mode; in the dB mode, a 1N4148 diode is inserted in series to provide correction for the temperature coefficient of the dB scale factor. Calibration of the meter is done by first adjust- ing offset pot R17 for a proper zero reading, then adjusting the R13 for an accurate readout at full scale. Calibration of the dB range is accomplished by adjusting R9 for the desired 0 dB reference point, then adjusting R14 for the desired dB scale factor (a scale of 10 counts per dB is convenient). Total power supply current for this circuit is typically 2.8 mA using a 7106-type ADC. A LOW POWER, HIGH INPUT IMPEDANCE dB METER Introduction The portable dB meter circuit featured here combines the func- tions of the AD636 rms converter, the AD589 voltage reference, and a µA776 low power operational amplifier. This meter offers excellent bandwidth and superior high and low level accuracy while consuming minimal power from a standard 9 volt transis- tor radio battery. In this circuit, the built-in buffer amplifier of the AD636 is used as a “bootstrapped” input stage increasing the normal 6.7 k Ω input Z to an input impedance of approximately 10 10 Ω. |
Podobny numer części - AD636J |
|
Podobny opis - AD636J |
|
|
Link URL |
Polityka prywatności |
ALLDATASHEET.PL |
Czy Alldatasheet okazała się pomocna? [ DONATE ] |
O Alldatasheet | Reklama | Kontakt | Polityka prywatności | Linki | Lista producentów All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |