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RF mixers ppt

RF signal Mixer Presentation

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RF mixers ppt

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  1. RF Mixers What are RF mixers? The end or first Parts of RF circuit nearest to an Antennathat mix or multiply RF input signal with LO. Translates signal’s frequency to the desired frequency bandfor transmission or further signal processing. Multiplier in time domain and adder in frequency domain.

  2. RF mixer operation & symbol • There are three ports to any RF mixer. • Up-conversionwith HPF for transmission and down- conversion with LPF for receiving .

  3. RF mixer circuits • There is an enormous variety of different types of circuits including: • Single diode mixer:is the simplest form available, mainly using Schottky diodes with very few electronic components. • BJT RF mixer: Typically this circuit will be used to convert signals from a HF down to a much LF. BJT RF mixer.

  4. RF mixer circuit • Basic FET mixer: • If dual there is dual gate MOSFET is used, these devices provide excellent performance. • There are many different circuits for FET mixers, each one having its own advantages and disadvantages. Basic FET mixer

  5. Types of RF mixer • Based on electronics component used in them: • Passive mixers: use passive components in the form of diodes as the switching element. As a result they cannot exhibit any gain, but can provide excellent levels of performance. • Active mixers: contains active electronic components like BJT & FET. Able to provide gain as well as proving the multiplication or RF mixing capability.

  6. Types of mixer • Based on whether they are balanced or not: • unbalanced RF mixer: made from single diode & simply mixes the two signals together and the output consists of the IF signals as well as significant levels of the original RF signal &that of the LO. • Single balanced: made from two diodes & has a single balancing circuit in between the input (RF & LO) ports of. The hybrid ports are mutually isolated. • Double balanced mixer: made from four diodes & has a double balancing circuit placed at both RF & LO ports.It can reduce the level of IMDby up to 75% when compared to a single diode unbalanced RF mixer.

  7. Types of mixers 4) Triple balanced mixer:   made from two double balanced mixers and as a result it is sometimes called a doubly double balanced mixer. • Has a Three balancing circuit placed at RF, LO & IF ports. • This allows for the IF signal to be available at two separate isolated terminals. • This improved isolationprovides much higher levels of IMD.

  8. RF mixer Parameters • For any system design the key parameters of a mixer are: • conversion gain/loss, isolation, and IMD (linearity). • In passivemixers; conversion loss: is the difference of power at input to output port. • CL = Prf – Pif; for Down-conversion mixer • CL = Pif – prf; for Up-conversion mixer • Typical values of CL can range from approximately 4.5 to 9 dB, depending on the mixer,

  9. Mixer parameter • In active mixers, conversion gain: is the ratio of power at output port to input ports. • CL = Prf / Pif; for Down-conversion mixer • Cl = Pif / prf ; for Up-conversion mixer. • Conversion gain of a typical active mixer is approximately +10 dB. • Isolation:- the difference in signal level between the power of an input signal and the power of the leaked power from that input signal to another port." When isolation is high, the amount of power leaked from one port to a different port is small.

  10. Mixer parameter • Intermodulation Distortion: is caused by non-linear behavior of the mixer.IMD occurs when two signals simultaneously enter the mixer’s IF or RF input port. • These two signals interact with each other and with the LO signal, which creates a non-(Additive, linear) &unboundeddistortion. • In a receiver, two-tone third-order IMD is a serious problem because it can generate third-order distortion products.

  11. Mixer parameter • The third-order distortion products are extremely close to the desired IF output frequency. No amount of filtering can remove these unwanted distortion products. • For any 1-dB increase in the input signal’s amplitude, the third-order products increase by 3dB. • The third-order input intercept point (TOI or IP3) is a accepted figure of merit used to describe a mixer’s capability to suppress third-order distortion products.

  12. RF Mixer applications • They are used in circuits from radio receivers and transmitters to radar systems, and in fact anywhere that RF signals are used. • These mixers can be used in a variety of different ways: • Frequency translation:  In receivers and transmitters to move the frequency of a signal from one band to another. One of the first major applications of this was in the Super-heterodyne radio receiver. • Phase comparison: To detect the phase difference between two signals.

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