Question

What are the SHDN, LNA in opamp
What are the TXCO
coding algorithm for binary and target search in bitwise modulated signal I and Q?

Answer 1

Answer:

SHDN - An active-low shutdown input, SHDN, disables the op-amp, placing its output in a high-impedance state. Most often the purpose of the shutdown pin is to idle the amplifier function and reduce its power consumption. When the op-amp is shut down it goes into a non-active mode where the quiescent current (Iq) is reduced by many orders of magnitude.

LNA - A low-noise amplifier (LNA) is an electronic amplifier that amplifies a very low-power signal without significantly degrading its signal-to-noise ratio. An amplifier will increase the power of both the signal and the noise present at its input, but the amplifier will also introduce some additional noise. The designed prototype LNA is based on the parallelization technique of Op-amps.

TXCO - A TCXO or a Temperature Compensated Crystal Oscillator is a crystal oscillator specially designed to operate in high-temperature environments. The oscillation frequency of a regular crystal oscillator changes/fluctuates as the temperature rises, resulting in an unstable oscillation frequency. TCXO's provide a stable oscillation frequency in high-temperature environments. To do so, they use a temperature compensation network that stabilizes the oscillation frequency at higher temperatures. It is a very stable master oscillator so that the frequencies indicated by the radio's display are accurate and stable. Most TCXO's have worst-case specifications around 1 ppm, some better, some a little worse.

Coding algorithm for binary and target search in bitwise modulated signal I and Q:

The simple concept of Modulation of I and Q Signals:

The term “I/Q” is an abbreviation for “in-phase” and “quadrature.” Unfortunately, we already have a terminology problem. First of all, “in-phase” and “quadrature” have no meaning on their own; phase is relative, and something can only be “in phase” or “out of phase” with reference to another signal or an established reference point. Furthermore, we now have the word “quadrature” applied to both a signal and the modulation/demodulation techniques associated with that signal.

In any event, “in-phase” and “quadrature” refer to two sinusoids that have the same frequency and are 90° out of phase. By convention, the I signal is a cosine waveform, and the Q signal is a sine waveform. As you know, a sine wave (without any additional phase) is shifted by 90° relative to a cosine wave. Another way to express this is that the sine and cosine waves are in quadrature.

The first thing to understand about I/Q signals is that they are always amplitude-modulated, not frequency- or phase-modulated.

I and Q signals on their own are not very interesting. The interesting thing happens when I and Q waveforms are added. It turns out that any form of modulation can be performed simply by varying the amplitude—only the amplitude—of I and Q signals, and then adding them together.

If you take I and Q signals of equal amplitude and add them, the result is a sinusoid with a phase that is exactly between the phase of the I signal and the phase of the Q signal.

The term “quadrature modulation” refers to modulation that is based on the summation of two signals that are in quadrature. In other words, it is I/Q-signal-based modulation. We’ll use QPSK as an example of how quadrature modulation works, and in the process, we’ll see how amplitude modulation of I/Q signals can produce phase shifts beyond 90°.the digital data stream is processed so that two consecutive bits become two parallel bits. Both of these bits will be transmitted simultaneously; in other words, QPSK allows one symbol to transfer two bits. The local oscillator generates the carrier sinusoid. The local oscillator signal itself becomes the I carrier, and a 90° phase shift is applied to create the Q carrier. The I and Q carriers are multiplied by the I and Q data streams, and the two signals resulting from these multiplications are summed to produce the QPSK-modulated waveform.

The I and Q data streams are amplitude-modulating the I and Q carriers, and as explained above, these individual amplitude modulations can be used to produce phase modulation in the final signal.If the I and Q data streams were typical digital signals extending from ground to some positive voltage, we would be applying on-off keying to the I and Q carriers, and our phase shift would be restricted to 45° in either direction. However, if the I and Q data streams are bipolar signals—i.e., if they swing between a negative voltage and a positive voltage—our “amplitude modulation” is actually inverting the carrier whenever the input data is logic low (because the negative input voltage multiplied by the carrier results in inversion).

This means that we will have four I/Q states:

• I normal and Q normal
• I normal and Q inverted
• I inverted and Q normal
• I inverted and Q inverted

As you can see, summation in these four cases produces exactly what we want to have in a QPSK signal: phase shifts of 45°, 135°, 225°, and 315°.

• I/Q signaling refers to the use of two sinusoids that have the same frequency and a relative phase shift of 90°.
• Amplitude, phase, and frequency modulation can be performed by summing amplitude-modulated I/Q signals.
• Quadrature modulation refers to modulation that involves I/Q signals.
• Quadrature phase-shift keying can be accomplished by adding I and Q carriers that have been individually multiplied, in accordance with the incoming digital data, by +1 or –1.

- usually using local search algorithms such as the binary switching algorithm.

- Additionally, even when the constellation is not binary, bit-wise soft decoding can be performed. This is attractive to reduce decoding complexity and it is widely used in practical receivers. For example, if we use uncoded QPSK and the target performance estimated using the blind phase search algorithm.

In above there is a simple concept of what Modulated signal I and Q and next what is the coding language used for it.