entc 3320
Download
Skip this Video
Download Presentation
ENTC 3320

Loading in 2 Seconds...

play fullscreen
1 / 33

ENTC 3320 - PowerPoint PPT Presentation


  • 245 Views
  • Uploaded on

ENTC 3320. Absolute Value. Half-Wave Rectifier. The inverting amplifier is converted into an ideal (linear precision) half-wave rectifier by adding two diodes. . - 0.6 V. 0 V.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'ENTC 3320' - waylon


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
entc 3320

ENTC 3320

Absolute Value

half wave rectifier
Half-Wave Rectifier
  • The inverting amplifier is converted into an ideal (linear precision) half-wave rectifier by adding two diodes.

- 0.6 V

0 V

slide3
When E, is positive, diode D1 conducts, causing the op amp’s output voltage, VOA,to go negative by one diode drop (-0.6 V).
    • This forces diode D2 to be reverse biased.
      • The circuit’s output voltage Vo equals zero because input current I flows through D1.
      • For all practical purposes, no current flows through Rf and therefore Vo = 0.
slide4
Note the load is modeled by a resistor RLand must always be resistive.
    • If the load is a capacitor, inductor, voltage, or current source, then V0 will not equal zero.
slide6
This causes D2 to conduct.
    • The circuit then acts like an inverter, since Rf = Ri, and Vo =+E1.
      • Since the (—) input is at ground potential, diode D1 is reverse biased.
      • Input current is set by E/Ri and gain by ─Rf/Ri.
      • Remember that this gain equation applies only for negative inputs, and Vo can only be positive or zero.
slide7
Circuit operation is summarized by the following waveshapes.
  • Vo can only go positive in a linear response to negative inputs.
slide9
The most important property of this linear half-wave rectifier will now be examined.
  • An ordinary silicon diode or even a hot-carrier diode requires a few tenths of volts to become forward biased.
    • Any signal voltage below this threshold voltage cannot be rectified.
    • However, by connecting the diode in the feedback loop of an op amp, the threshold voltage of the diode is essentially eliminated.
slide10
For example. in Fig. 7-2(b) let E, be a low voltage of —0.1 V. E, and R, convert this low voltage to a current that is conducted through D2.
    • VOA goes to whatever voltage is required to supply the necessary diode drop plus the voltage drop across R~. Thus millivolts of input voltage can be rectified, since the diode’s forward bias is supplied automatically by the negative feedback action of the op amp.
slide11
Finally, observe the waveshape of op amp output V~ in Fig. 7-3. When E~ crosses 0 V (going negative), V(~ jumps quickly from —0.6 V to +0.6 V as it switches from supplying the drop for D2 to supplying the drop for D1. This jump can be monitored by a differentiator to indicate the zero crossing. During the jump time the op amp operates open loop.
slide12
The diodes can be reversed as shown below.
    • Now only positive input signals are transmitted and inverted.
slide13
The output voltage Vo equals 0 V for all negative inputs.
    • Circuit operation is summarized by the plot of V~ and VOA versus E.
7 1 4 signal polarity separator
7-1.4 Signal Polarity Separator
  • The following circuit is an expansion of the previous circuits.
    • When E, is positive, diode D1 conducts and an output is obtained only on output V0,.
      • V0, is bound at 0 V.
    • When E, is negative. D2 conducts, V0. = —(—E,) = +E,. and V0~ is bound at 0 V.
introduction
Introduction
  • The precision full-wave rectifier transmits one polarity of the input signal and inverts the other.
    • Thus both half-cycles of an alternating voltage are transmitted but are converted to a single polarity of the circuirs output.
slide20
The precision full-wave rectifier can rectify input voltages with millivolt amplitudes.
    • This type of circuit is useful to prepare signals for multiplication, averaging, or demodulation.
slide22
The precision rectifier is also called an absolute-value circuit.
    • The absolute value of a number (or voltage) is equal to its magnitude regardless of sign.
slide23
For example, the absolute values of |+2 | and |2 | are +2.
    • The symbol | | means “absolute value of.”
      • In a precision rectifier circuit the output is either negative or positive, depending on how the diodes are installed.
slide26
Three types of precision rectifiers will be presented.
    • The first is inexpensive because it uses two op amps. two diodes, and five equal resistors.
      • Unfortunately. it does not have high input resistance.
    • ~o a second type is given that does have high input resistance but requires resistors that are precisely proportioned but not all equal.
      • Neither type has a summing node at virtual ground potential.
full wave precision rectifier with equal resistors
Full-wave precision rectifier with equal resistors.
  • Thefirst type of precision full-wave rectifier or absolute-value circuit is shown below.
slide31
Figure 7-8(a) shows current directions and voltage polarities for po~iti~e input signals. Diode D~ conducts so that both amps A and B act as inverters, and V0 = +E,.
    • Figure 7-8(b) shows that for negative input voltages, diode D.~ conducts. Input rent I divides as shown, so that op amp B acts as an inverter. Thus output voltage V0 positive for either polarity of input E, and V0 is equal to the absolute value of E,
ad