Motore di ricerca datesheet componenti elettronici |
|
AD650S Scheda tecnica(PDF) 4 Page - Analog Devices |
|
AD650S Scheda tecnica(HTML) 4 Page - Analog Devices |
4 / 12 page AD650 REV. C –4– CIRCUIT OPERATION UNIPOLAR CONFIGURATION The AD650 is a charge balance voltage-to-frequency converter. In the connection diagram shown in Figure 1, or the block diagram of Figure 2a, the input signal is converted into an equivalent cur- rent by the input resistance RIN. This current is exactly balanced by an internal feedback current delivered in short, timed bursts from the switched 1 mA internal current source. These bursts of current may be thought of as precisely defined packets of charge. The required number of charge packets, each producing one pulse of the output transistor, depends upon the amplitude of the input signal. Since the number of charge packets delivered per unit time is dependent on the input signal amplitude, a linear voltage-to-frequency transformation will be accomplished. The frequency output is furnished via an open collector transistor. A more rigorous analysis demonstrates how the charge balance voltage-to-frequency conversion takes place. A block diagram of the device arranged as a V-to-F converter is shown in Figure 2a. The unit is comprised of an input integra- tor, a current source and steering switch, a comparator and a one-shot. When the output of the one-shot is low, the current steering switch S1 diverts all the current to the output of the op amp; this is called the Integration Period. When the one-shot has been triggered and its output is high, the switch S1 diverts all the current to the summing junction of the op amp; this is called the Reset Period. The two different states are shown in Figure 2 along with the various branch currents. It should be noted that the output current from the op amp is the same for either state, thus minimizing transients. Figure 1. Connection Diagram for V/F Conversion, Positive Input Voltage Figure 2a. Block Diagram Figure 2b. Reset Mode Figure 2c. Integrate Mode Figure 2d. Voltage Across CINT The positive input voltage develops a current (IIN = VIN/RIN) which charges the integrator capacitor CINT. As charge builds up on CINT, the output voltage of the integrator ramps downward towards ground. When the integrator output voltage (Pin 1) crosses the comparator threshold (–0.6 volt) the comparator triggers the one shot, whose time period, tOS is determined by the one shot capacitor COS. Specifically, the one shot time period is: tOS = COS × 6.8 ×103 sec /F + 3.0 ×10–7 sec (1) The Reset Period is initiated as soon as the integrator output voltage crosses the comparator threshold, and the integrator ramps upward by an amount: ∆V = t OS • dV dt = tOS CINT 1mA – IN () (2) After the Reset Period has ended, the device starts another Inte- gration Period, as shown in Figure 2, and starts ramping downward again. The amount of time required to reach the comparator threshold is given as: TI = ∆V dV dt = tOS/CINT(1 mA – IIN ) IN /CINT = tOS 1 mA IIN –1 (3) The output frequency is now given as: fOUT = 1 tOS + TI = IIN tOS ×1 mA = 0.15 F • Hz A VIN /RIN COS + 4.4 ×10–11F (4) Note that CINT, the integration capacitor has no effect on the transfer relation, but merely determines the amplitude of the sawtooth signal out of the integrator. One Shot Timing A key part of the preceding analysis is the one shot time period that was given in equation (1). This time period can be broken down into approximately 300 ns of propagation delay, and a sec- ond time segment dependent linearly on timing capacitor COS. When the one shot is triggered, a voltage switch that holds Pin 6 |
Codice articolo simile - AD650S |
|
Descrizione simile - AD650S |
|
|
Link URL |
Privacy Policy |
ALLDATASHEETIT.COM |
Lei ha avuto il aiuto da alldatasheet? [ DONATE ] |
Di alldatasheet | Richest di pubblicita | contatti | Privacy Policy | scambio Link | Ricerca produttore 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 |