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Home , AM broadcasting, Radio receiver

Analog Circuits and Systems

Prof. K Radhakrishna Rao

Lecture 2 Role of Analog Processing in Electronic Products – Part 1

1 Structure of an electronic product

2 Electronic Products o Process analog and o This involve transmission and reception of signals and data o It is generally necessary to code signal and data to transmit over channels o Transmission can be over wires or o Processing and storage are efficient in digital form o Several human interface technologies are available

3 Products considered o Receiver o o Cell Phone o ECG

4 o AM Receiver o FM Receiver

5 Radio waves are classified as o Low (LF): 30 kHz – 300 kHz, o (MF): 300 kHz – 3 MHz, o (HF): 3 MHz – 30 MHz, o (VHF): 30 MHz – 300 MHz, o (UHF): 300 MHz – 3 GHz, o Super high frequency (SHF): 3 GHz – 30 GHz, o Extremely high frequency (EHF): 30 GHz to 300 GHz.

6 Radio o one-way wireless transmission over radio waves to reach a wide audience o takes place in MF (300 kHz – 3 MHz), HF (3 MHz – 30 MHz) and VHF (30 MHz – 300 MHz) regions

7 Major modes of o (single tone) represented by

Vtp sin(ωφ+ ) PM ( Analog) where φ = in radians PSK ( Digital) QPSK( Digital)

FM ( Analog) ω = frequency in rad/sec FSK ( Digital)

AM, DSB ( Analog) V = peak magnitude in p ASK ( Digital)

8 AM broadcasting

o of the carrier signal is varied in response to the amplitude of the signal to be transmitted o Amplitude is done by a unit called mixer (nothing but a multiplier) which produces an output

output=+( Vpc V pm sinωω m t )sin c t Vpm where ωm is the modulating frequency = m is known as the Vpc ω is the carrier frequency c modulation index. Vpc is the amplitude of the carrier and

Vpm is the amplitude of the modulating signal

9 AM broadcasting

Carrier Signal

Modulating Sine Wave Signal

Amplitude Modulated Signal

10 AM broadcasting o range: 540 kHz -1.7 MHz ◦ can be received over thousands of miles (especially at night) ◦ very sensitive to atmospheric conditions and solar activity o Short wave range: 1.6 MHz – 30 MHz

11 AM Receiver

12 AM Receiver o with RF : Tunable band pass filter cum amplifier o Mixer: Shifts the variable carrier frequency to a lower fixed . It is a multiplier of carrier and the local

oscillator generated sine wave (c + IF) where IF = 455 kHz o IF amplifier: Tuned amplifier with centre frequency at IF. = 2 x signal bandwidth o AM : AM demodulator (multiplier/ peak detector) o AGC (Automatic Control): Uses the IF signal strength information to control the gains of RF amplifier/mixer/ IF amplifier o Power amplifier feeds the speakers 13 FM Broadcasting o Frequency of the carrier signal is varied in response to the amplitude of the signal to be transmitted o is achieved by designing an oscillator whose frequency is controlled by the modulating signal using controlled oscillator (VCO) o FM broadcasting is over 88 MHz – 108 MHz o FM channels are separated by 0.2 MHz

14 FM Broadcasting

VCO=+ Vpcsin(ωωω cΔ d sin m t) t

where ωc is the carrier frequency,

Δωd is the frequency deviation

and ωm is the modulating frequency.

15 FM Receiver

16 FM Receiver o Antenna with RF amplifier: Tunable band pass filter cum amplifier o Mixer: Shifts the carrier frequency that is variable to a lower intermediate frequency. It is a multiplier of carrier and the generated sine wave (c + IF) where IF = 10.7 MHz o IF amplifier: Tuned amplifier with centre frequency at IF. Bandwidth = 2 x signal bandwidth o FM detector: FM demodulator (Phase Locked Loop/frequency discriminator) o AGC (): Uses the IF signal strength information to control the gains of RF amplifier/mixer/IF amplifier o Stereo Power Amplifier

17 Modem o Short for MOdulator - DEModulator o The Modem is a hardware device that enables a to send and receive information over lines, or any other communication channel o It converts the digital data used by the computer into an used on phone lines, and converts the received analog signal into digital data to be used by the computer o are asynchronous devices: the device transmits data in an intermittent stream of small packets. Once received, the receiving system then takes the data in the packets and reassembles it into a form the computer can use.

18 Modem (contd..) o 1 or more byte/s (8 bits) is transferred within 1 packet, which is equivalent to one character. o For the computer to receive information each packet must contain a Start and a Stop bit; therefore, the complete packet would be 10 bits.

19 Generic Functional Block Diagram of a Modem

20