PowerPoint Presentation

ADNU ECEM416Radio Receiversjjcb8/8/2013ADNU ECEM416OutlineIntroductionReceiver typesSuperheterodyne ReceiverAM ReceiverFM ReceiverTV ReceiverSoftware-Defined Radio(SDR)jjcb8/8/2013ADNU ECEM416ReceiversCollect signal from the medium in which it existAble to identify and select desired signal and to provide sufficient amplification to recover the modulating signalFunctions:Transduction and matchingSelection of desired signalsRejection of undesired signalsAmplification be very large factorsDemodulationIntroductionjjcb8/8/2013ADNU ECEM416Characteristics:IntroductionjjcbSelectivity: Q and BandwidthAbility to amplify weak signalObtained by using LC tuned circuit Controlling Q setting desired selectivitycontrolling the bandwidth Optimum bandwidth wide enough to pass the signal but narrow enough to eliminate signals on adjacent frequencies8/8/2013ADNU ECEM416jjcbSelectivity: Q and Bandwidth

8/8/2013ADNU ECEM416Characteristics:IntroductionjjcbSelectivity: Shape FactorSkirts sides of a tuned circuit responseSteepness of the skirt or skirt selectivityExpressed as the shape factorLower shape factor higher sensitivity

SF = Shape factor (unitless)B(-60 dB) = bandwidth 60 dB below maximum signal levelB(-3 dB) = bandwidth 3 dB below maximum signal level8/8/2013ADNU ECEM416Characteristics:IntroductionjjcbSensitivityAbility to pick up weak signalsHigh gain High sensitivitythe minimum input RF signal to a receiver required to produce a specified audio signal at output.The ability to drive the output transducer (e.g., speaker) to an acceptable levelMeasured in microvolt or decibels above 1mW

8/8/2013ADNU ECEM416Receiver TypesSimplest Radio Receiverjjcb

8/8/2013ADNU ECEM416Receiver Types

Tuned Radio-Frequency(TRF)jjcb8/8/2013

ADNU ECEM416Receiver TypesTuned Radio-Frequency(TRF)jjcb8/8/2013ADNU ECEM416Receiver TypesSimple receiver2 or 3 RF amplifier, all tuning together, are used to improved the sensitivity.Greater the number of tuned circuits, the narrower the bandwidth and steeper the skirts

jjcbTuned Radio-Frequency(TRF)Tracking the tuned circuitsSelectivity is bad at higher frequencyInstability

Disadvantages:8/8/2013ADNU ECEM416Receiver TypesSuperheterodyne receiverjjcb

8/8/2013ADNU ECEM416jjcbReceiver Typesconvert all incoming signals to a lower frequency, known as the intermediate frequency (IF), at which a single set of amplifiers is used to provide a fixed level of sensitivity and selectivity.Gain and selectivity are obtained in the IF amplifiers.The key circuit is the mixer, which acts like a simple amplitude modulator to produce sum and difference frequencies.The incoming signal is mixed with a local oscillator signal.

Superheterodyne receiver8/8/2013ADNU ECEM416jjcbSuperheterodyne ReceiverRF stageMixer and Local oscillatorIF AmplifierDetector/DemodulatorAutomatic Gain ControlAudio Amplifier

Main sections: 8/8/2013ADNU ECEM416jjcbused mainly to select the wanted frequency, to reject interference such as the image frequency and (especially at high frequencies) to reduce the noise figure of the receiver. The antenna picks up the weak radio signal and feeds it to the RF amplifier, also called a low-noise amplifier.RF amplifiers provide some initial gain and selectivity and are sometimes called preselectors.Bipolar and FETs can be used as RF amplifiers.may or may not be required.

RF AmplifierSuperheterodyne Receiver8/8/2013ADNU ECEM416jjcbRF AmplifierSuperheterodyne ReceiverAdvantage:Better sensitivityImproved image frequency rejectionImproved signal-to-noise ratioImproved rejection of adjacent unwanted signalsRejection of spurious signalsMinimize the oscillator radiation

8/8/2013ADNU ECEM416jjcbSuperheterodyne ReceiverA nonlinear device having two sets of input terminals and one set of output terminalsOne input is from the RF amplifier and the other is from the local oscillator Most common type are the bipolar transistor, FET and MOSFET.The mixer output is the input signal, the local oscillator signal, and the sum and difference frequencies of these signals.

Mixer and Local Oscillator8/8/2013ADNU ECEM416jjcbSuperheterodyne ReceiverFrequency conversion the process of translating a modulated signal to a higher or lower frequency while retaining all the originally transmitted information.form of amplitude modulation carried out by a mixer circuit or converter.In radio receivers, high-frequency signals are converted to a lower, intermediate frequency. This is called down conversion.The function performed by the mixer is called heterodyning.

Mixer: How it Works8/8/2013

ADNU ECEM416jjcbSuperheterodyne ReceiverMixer: How it Works8/8/2013ADNU ECEM416jjcbSuperheterodyne ReceiverTypes of Mixers:Diode MixersDoubly Balanced MixerFET MixersIC MixersImage Reject MixerMixer: How it Works8/8/2013ADNU ECEM416jjcbSuperheterodyne ReceiverA fixed-frequency amplifier with the very important function of rejecting adjacent unwanted frequency.The output of the mixer is an IF signal containing the same modulation that appeared on the input RF signal.Usually two or more IF amplifiers are used to provide adequate receiver gain.Since the intermediate frequency is usually lower than the input frequency, IF amplifiers are easier to design and good selectivity is easier to obtain.

IF Amplifier8/8/2013ADNU ECEM416jjcbSuperheterodyne ReceiverIF amplifiers are tuned class A circuits capable of providing gain in the 10- to 30-dB range.Ferrite-core transformers are used for coupling between stages.Selectivity is provided by tuned circuits.

IF Amplifier

8/8/2013ADNU ECEM416jjcbSuperheterodyne ReceiverChanging the amount of coupling between the primary and secondary windings allows the desired amount of bandwidth to be obtained. Degree of couplingUndercouplingCritical couplingOptimumcouplingOvercoupling

IF Amplifier: Coupled Circuit Selectivity8/8/2013ADNU ECEM416jjcbSuperheterodyne ReceiverImagePotentially interfering RF signal that is spaced from the desired incoming signal by a frequency 2 times the intermediate frequency above or below the incoming frequencyIntermediate Frequency and Images8/8/2013ADNU ECEM416jjcbSuperheterodyne ReceiverThe primary objective in the design of an IF stage is to obtain good selectivity. Narrow-band selectivity is best obtained at lower frequencies.At low frequencies, circuits are more stable with high gain. At low frequencies, image interference is possible. Intermediate Frequency and Images8/8/2013ADNU ECEM416jjcbSuperheterodyne ReceiverIntermediate Frequency and Images

8/8/2013ADNU ECEM416jjcbSuperheterodyne ReceiverIntermediate Frequency and ImagesTo eliminate the image:The IF is made as high as possible for effective elimination of the image problem, yet low enough to prevent design problems.Using Dual-conversion that has two mixer, two oscillator and two IF.Using Direct Conversion, not using a IF filter.8/8/2013ADNU ECEM416jjcbSuperheterodyne ReceiverThe highly amplified IF signal is finally applied to the demodulator, which recovers the original modulating information.The demodulator may be a diode detector (for AM), a quadrature detector (for FM), or a product detector (for SSB).The output of the demodulator is then usually fed to an audio amplifier.Demodulators/Detectors8/8/2013ADNU ECEM416jjcbSuperheterodyne ReceiverThe recovered signal from the output of the modulator that is rectified and filtered into a DC voltage by a circuit is called AGC circuit.Typically, receivers are designed with very high gain so that weak signals can be reliably received. However, applying a very high-amplitude signal to a receiver causes the circuits to be overdriven, producing distortion and reducing intelligibility. With AGC, the overall gain of the receiver is automatically adjusted depending on the input signal level. gives the receiver a very wide dynamic range.

Automatic Gain Control8/8/2013ADNU ECEM416jjcbSuperheterodyne ReceiverThe gain of a bipolar transistor amplifier is proportional to the amount of collector current flowing. Two methods of applying AGC are as follows:The gain can be decreased by decreasing the collector current. This is called reverse AGC.The gain can be reduced by increasing the collector current. A stronger signal increases AGC voltage and base current and, in turn, increases collector current, reducing the gain. This method of gain control is known as forward AGC.

Automatic Gain Control: Controlling Circuit Gain8/8/2013ADNU ECEM416jjcbSuperheterodyne ReceiverAutomatic Gain Control: Controlling Circuit Gain

8/8/2013ADNU ECEM416jjcbAM Receiver

8/8/2013ADNU ECEM416jjcbAM ReceiverDemodulationDiode DetectorSimplest and most widely used AM demodulatorOften termed as envelope detector circuit. If the RC time constant in a diode detector is too long, the capacitor discharge will be too slow to follow the faster changes in the modulating signal. It is referred to as diagonal distortion.

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ADNU ECEM416jjcbAM ReceiverDiode Detector8/8/2013ADNU ECEM416jjcbAM ReceiverDiode Detector: How it WorksOn positive alternations of the AM signal, the capacitor charges quickly to the peak value of pulses passed by the diode.When the pulse voltage drops to zero, the capacitor discharges into the resistor.The time constant of the capacitor and resistor is long compared to the period of the carrier.The capacitor discharges only slightly when the diode is not conducting.The resulting waveform across the capacitor is a close approximation to the original modulating signal. 8/8/2013ADNU ECEM416jjcbAM ReceiverDemodulationDiode DetectorAdvantages:Handle relatively high power signals.Distortion levels are acceptable for most AM applications. It decreases as the amplitude increases.Highly efficient.Develop a readily usable dc voltage for AGC circuits.8/8/2013ADNU ECEM416jjcbAM ReceiverDemodulationDiode DetectorDisadvantage:Power is absorbed from the tuned circuit by the diode circuit that reduces the Q and selectivity of the tuned input circuit.No amplification occur.

8/8/2013ADNU ECEM416jjcbAM ReceiverDemodulationSynchronous DetectorsUse an internal clock signal at the carrier frequency in the receiver to switch the AM signal off and on, producing rectification similar to that in standard detector.Synchronous detectors or coherent detectors have less distortion and a better signal-to-noise ratio than standard diode detectors.The signal producing the switching action should be perfectly in phase with the received AM carrier

8/8/2013ADNU ECEM416jjcbAM ReceiverSynchronous Detectors

8/8/2013ADNU ECEM416jjcbAM ReceiverSSB DemodulationTo recover the intelligence in a DSB or SSB signal, the carrier that was suppressed at the receiver must be reinserted.A product detector is a balanced modulator used in a receiver to recover the modulating signal.Any balanced modulator can be used as a product detector to demodulate SSB signals.

8/8/2013ADNU ECEM416jjcbAM ReceiverSSB Demodulation

8/8/2013ADNU ECEM416jjcbFM ReceiverLimiterA circuit whose output is a constant amplitude for all inputs above a critical value.Remove any unwanted amplitude modulation and amplitude variation due to noise.Provides AGC action because it provides constant input level to the detector.

8/8/2013ADNU ECEM416jjcbFM ReceiverLimiter

8/8/2013ADNU ECEM416jjcbFM ReceiverFM discriminator/detectorSlope DetectorSimplest frequency demodulator.Makes use of a tuned circuit and a diode detector to convert frequency variations to voltage variations.The main difficulty with slope detectors lies in tuning them.

8/8/2013ADNU ECEM416jjcbFM ReceiverSlope Detector

8/8/2013ADNU ECEM416jjcbFM ReceiverPulse-Averaging DiscriminatorsA pulse-averaging discriminator uses a zero crossing detector, a one shot multivibrator and a low-pass filter in order to recover the original modulating signal.The pulse-averaging discriminator is a very high-quality frequency demodulator.Originally this discriminator was limited to expensive telemetry and industrial control applications.With availability of low-cost ICs, this discriminator is used in many electronic products.

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ADNU ECEM416jjcbFM ReceiverPulse-Averaging Discriminators8/8/2013ADNU ECEM416jjcbFM ReceiverFM discriminator/detectorQuadrature DetectorsThe quadrature detector is probably the single most widely used FM demodulator.The quadrature detector is primarily used in TV demodulation.This detector is used in some FM radio stations.The quadrature detector uses a phase-shift circuit to produce a phase shift of 90 degrees at the unmodulated carrier frequency.

8/8/2013ADNU ECEM416jjcbFM ReceiverQuadrature Detectors

8/8/2013ADNU ECEM416jjcbFM ReceiverFM discriminator/detectorPhase-Locked LoopsA phase-locked loop (PLL) is a frequency- or phase-sensitive feedback control circuit used in frequency demodulation, frequency synthesizers, and various filtering and signal-detection applications. PLLs have three basic elements. They are:Phase detectorLow-pass filterVoltage-controlled oscillator

8/8/2013ADNU ECEM416jjcbFM ReceiverPhase-Locked Loops

8/8/2013ADNU ECEM416jjcbFM ReceiverPhase-Locked LoopsThe primary job of the phase detector is to compare the two input signals and generate an output signal that, when filtered, will control the VCO. If there is a phase or frequency difference between the FM input and VCO signals, the phase detector output varies in proportion to the difference. The filtered output adjusts the VCO frequency in an attempt to correct for the original frequency or phase difference.

8/8/2013ADNU ECEM416jjcbFM ReceiverPhase-Locked LoopsThis dc control voltage, called the error signal, is also the feedback in this circuit.When no input signal is applied, the phase detector and low-pass filter outputs are zero. The VCO then operates at what is called the free-running frequency, its normal operating frequency as determined by internal frequency-determining components.

8/8/2013ADNU ECEM416jjcbFM ReceiverPhase-Locked LoopsThis dc control voltage, called the error signal, is also the feedback in this circuit.When no input signal is applied, the phase detector and low-pass filter outputs are zero. The VCO then operates at what is called the free-running frequency, its normal operating frequency as determined by internal frequency-determining components.

8/8/2013ADNU ECEM416jjcbTV ReceiverBackground:Maximum modulating rate for video signal is 4MHzAllowable bandwidth per radio station is 6MHz.The lower sideband extends to 1.25MHz. The upper sideband is transmitted in full.Vestigial-sideband operation

8/8/2013ADNU ECEM416jjcbTV ReceiverBackground:Lower VHF BandUpper VHF BandUHF BandChannelLowest Freq.(Mhz)ChannelLowest Freq.(Mhz)ChannelLowest Freq.(Mhz)25471741447036081802453046691863459057610192446506821119854710122046477013210698008/8/2013ADNU ECEM416jjcbTV ReceiverBackground:

8/8/2013ADNU ECEM416jjcbTV ReceiverReceiverUtilizes superheterodyne principleHandle video and synchronizing signals and audio.How it works:Incoming signal is selected and amplified by the RF amplifierStepped down to the IF frequency by the mixer-local oscillator and.IF amplifiers handle the composite signal TV signals.8/8/2013ADNU ECEM416jjcbTV Receiver

8/8/2013ADNU ECEM416jjcbTV ReceiverHow it works (cont.):Video detector separates the sound and video signals.The sound signal detected is the FM signal and send to FM receiver(sound channel block).The output of the video detector is the video(plus sync) signal.The video signal is amplified in the video amplifier and controls the strength of the beam that is scanning the phosphor of the CRT.The sync precisely controls the horizontal and vertical movement of the electron beam.8/8/2013ADNU ECEM416jjcbTV ReceiverTunerContains RF amplifier, mixer and local oscillatorFor UHF, no RF amplifier is needed because of poor noise performance at high frequency

8/8/2013ADNU ECEM416jjcbTV ReceiverStagger TuningCascading a number of tuned bandpass filters each having slightly offset bandpass frequency to form a wider flat bandpass with steep high and low frequency roll-off skirts.

8/8/2013ADNU ECEM416jjcbTV ReceiverIF AmplifiersIntercarrier system is a system that process the sound and the video in the same IF stage.Same function as the regular radio reciever: provide the bulk of the sets sensitivity and amplification.Standard IF frequencies.45.75 MHz picture carrier41.25 MHz(45.75 minus 4.5MHz) sound carrier8/8/2013ADNU ECEM416jjcbTV ReceiverSAW FiltersExtremely high Q filters often used in TV and radar application. rely on the surface effects in a piezoelectric material.

8/8/2013ADNU ECEM416jjcbTV ReceiverWavetrapAlso called trapHigh Q bandstop circuit that attenuates a narrow band of frequencies

8/8/2013ADNU ECEM416jjcbTV ReceiverVideo Section

8/8/2013ADNU ECEM416jjcbTV ReceiverColor Receiver

8/8/2013ADNU ECEM416jjcbSoftware-Defined RadioA software-defined radio (SDR) is a receiver in which most of the functions are performed by a digital signal processor (DSP).The benefits of SDRs are improved performance and flexibility. The receiver characteristics (type of modulation, selectivity, etc.) can be easily changed by running a different program. Radio with functionality defined by softwareProgrammable on-board processing units for satellitesCognitive radios to avoid interference8/8/2013ADNU ECEM416jjcbSoftware-Defined RadioADCs and DACs placed next to the antennaADCs and DACs directly connected to FPGA or DSPGeneral purpose machines for further processingData delivered to applicationsIdeal SCR:

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