circuit - RF Cafe Forums
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Post subject: circuit
Unread postPosted: Mon Jul 18, 2005 9:53 am
Joined: Mon Jul 18, 2005 9:44 am
kindly answer the difference between the following circuits mixer, AM modulator, multiplier , sampling
Unread postPosted: Mon Jul 18, 2005 12:51 pm
Joined: Mon Jun 27, 2005 2:02 pm
Multuplier is a device or circuit that multiplies the input frequency, usually is implemented with Schottky diodes. This device or circuit should reject the fundamental and odd/even harmonics at its output and pass only the second harmonic.
Mixer is a device or circuit that converts a frequency to another frequency by means of doing a multiplication with a local oscillator frequency. The output of the mixer are the sum and difference of the local oscillator and input frequency. The mixer should reject the other frequency (would it be the sum or difference), this is usually done by connecting a BPF (Band-Pass Filter) at the output of the mixer. Mixer can be used for up-conversion and for down-conversion. Mixers can be implemented with Schottky dioes and Baluns or with active devices such as FETs
AM Modulator is a circuit or device that performs amplitude modulation over an input signal (Usually some kind of information signal: data, image or voice). The inputs to the AM Modulator are the information signal and a constanst frequency carrier signal. The modulation is done by changing the amplitude of a carrier signal according to the information signal (mixing). The output is a signal at the carrier frequency with amplitude that follows that shape of the information signal.
Sampling is the process which is used to sample any kind of information. According to the nyquist theorem it should be done at a frequency that is at least twice high than the frequency of the sampled signal: fs=2*fm
fs- sampling signal
fm - sampled signal