The mixer is generally used in what areas?

First, the principle of the mixer and literacy

( 1 ) Noise Figure

The noise is defined as the mixer : NF = Pno / Pso Pno noise temperature when the input port is standard at all frequencies when the temperature is T0 = 290K, information is transmitted to the output port of the total noise power used . Pno including thermal noise source , the internal loss resistance thermal noise , shot noise and the device current mixer local oscillator phase noise. Noise -owned Pso is only useful signal input at the output generated by power .

( 2 ) Conversion Loss

Mixer conversion loss is defined as the mixer RF input port of the microwave signal power and frequency output of the signal power ratio . Mainly by circuit mismatch loss , inherent diode junction conductance net loss and non-linear conversion loss and other causes.

(3) 1dB compression point

Under normal operating conditions, the RF input level is far below the level of the oscillator , then the output frequency changes linearly with the RF input when the RF level to a certain extent , with the IF output of the RF input increases slowed, mixer saturation . RF input power which deviate from linear frequency output 1dB when the mixer 's 1dB compression point . For the same structure mixer , 1dB compression point depends on the size and power of the local oscillator diode characteristics , generally lower than the LO power 6dB.

( 4 ) Dynamic range

Dynamic range refers to the microwave mixer normal operation power range . The lower limit varies mixer application environment varies, the upper limit by the RF input power saturation limit, generally corresponds to the mixer 1dB compression point .

( 5 ) two-tone third-order intermodulation

If there are two similar frequencies fs1 and fs2 microwave signal and local oscillator input to the mixer fLO together , due to the nonlinear effect of the mixer will generate intermodulation , which may appear in the third-order intermodulation output frequency near places , fall within the IF passband , causing interference , usually third-order intermodulation rejection ratio to describe , that the useful signal power and the third-order intermodulation signal power ratio , usually expressed as dBc. IF power because power is proportional with the input when the input signal is reduced microwave 1dB, third-order intermodulation signal rejection ratio increased 2dB.

( 6 ) Isolation

Mixer means isolated isolation between ports each frequency , including the isolation of the oscillator and RF , LO and IF, and RF and IF between . Defined as the vibration isolation or RF signal leakage to the power and input power than any other port in dB.

( 7 ) LO power

Mixer local oscillator power is the best working state required local oscillator power . In principle LO power greater dynamic range increases, improving linearity (1dB compression point rise in third-order intermodulation factor improvement ) .

( 8 ) port VSWR

Port VSWR directly affect the mixer used in the system , which is a parameter with the power , the frequency change.

( 9 ) the residual DC offset voltage IF

When the mixer as a phase detector when only one input , the output should be zero . However, due to the mixing tube is not satisfactory or balun pair imbalance causes a DC voltage at the IF output , ie IF residual DC offset voltage. The residual DC offset voltage will affect the phase accuracy.

Second, the application of the mixer

( 1 ) Frequency conversion : This is a well-known use of the mixer. Commonly used double-balanced mixers and three balanced mixer mixer is generally used in where ?

Since three balanced mixer using two diode bridge . Three ports have the transformer , so the local oscillator, RF and IF bandwidth of up to several octaves , and large dynamic range , low distortion , high isolation . But its high manufacturing costs , process complexity , and thus higher prices .

( 2 ) Phase : Theoretically all is DC-coupled IF mixer can be used as a phase detector used. The same two frequencies , consistent with the magnitude of the RF signal applied to the mixer LO and RF ports, with two intermediate frequency signal output terminal becomes a DC voltage difference . When two sinusoidal signals , the phase difference changes with sinusoidal output , when the two when the input signal is a square wave , triangle wave phase output compared . Recommend the use of standard power near the LO power , the input power is too large , it will increase the DC bias voltage is too small, the output level is too low .

( 3 ) Variable Attenuator / Switch : These mixers also requires intermediate DC-coupled . Signals between the mixer LO port and RF port frequency transmission loss is the current size of the control . When the control current is zero , the transmission loss to the RF oscillator is the isolation , when the control current of 20mA or more, i.e., the transmission loss of the insertion loss of the mixer . Thus , you can use positive or negative current to form a continuous control range of about 30dB variable attenuator changes and variations within the scope of the entire port VSWR little change . Similarly, the square wave control switch can be formed .

( 4 ) phase modulator (BPSK): IF these mixers also require DC-coupled . Signal at the mixer LO port and inter- port RF transmission frequency current phase is determined by the polarity control . IF control port alternately changing the polarity of the current phase will follow the output RF signal alternating at 0 ° and 180 °, the two states .

( 5 ) quadrature phase shift keying modulation : QPSK is composed of two BPSK, a bridge 90 and a 0 ° power splitter constituted .

I / Q modulator / demodulator modulation and demodulation process is actually antagonistic to each other , the system is reversible . This introduces I / Q demodulator , I / Q demodulator consists of two mixers, a bridge and a 90 degree phase splitters with composition.

( 6 ) image rejection mixer : the image frequency suppression filters are generally fixed bandwidth. But when the signal frequency is changed , the mirror ratio also changes frequently , the filter may be removed from the band suppression . In the multi-channel frequency-agile receiver system or systems, this filter will lose effect. Then using the image rejection mixer , when the local oscillator frequency changes due to internal phase mixer circuit with the relationship , the frequency range is suppressed mirror will also change , it can still play the role of image rejection . As the characteristics of the circuit is not entirely satisfactory , the presence of amplitude imbalance and phase imbalance may cause the electrical properties of the image rejection mixer deterioration occurs , the next picture shows the amplitude imbalance and phase imbalance are described on the electrical properties of sound.

( 7 ) a single sideband modulator : In a multichannel transmission system , the baseband frequency , if the ordinary low frequency shifting mixer , then the channel bandwidth in the two sidebands , which affects the use of spectrum resources . Then sideband modulator can be used to suppress the unwanted sideband , the basic structure of the two mixers , a 90-degree power splitter and an in-phase power splitter . The quadrature base band signal into two quadrature with the two oscillator mixing signals , using a phase offset technique to suppress undesired sidebands because the vibration isolation of the mixer itself be suppressed .