difference between analog ic and rfic
The most fundamental difference between low-frequency
analog and microwave design is that in microwave design, transmission line
concepts are important, while in low-frequency analog design, they are not.
This will have implications for the choice of impedance levels, as well as how
signal size, noise, and distortion are described.
On-chip dimensions are small, so even at RF frequencies (0.1–5 GHz),
transistors and other devices may not need to be connected by transmission
lines (i.e., the lengths of the interconnects may not be a significant fraction of
a wavelength). However, at the chip boundaries, or when traversing a significant
fraction of a wavelength on chip, transmission line theory becomes very
important. Thus, on chip we can usually make use of analog design concepts,
although, in practice, microwave design concepts are often used. At the chip
interfaces with the outside world, we must treat it like a microwave circuit
any comments ?
Re: difference between analog and rfic
In low-frequency analog design, input impedance is usually very high (ideally
infinity), while output impedance is low (ideally zero). For example, an operational
amplifier can be used as a buffer because its high input impedance does
not affect the circuit to which it is connected, and its low output impedance
can drive a measurement device efficiently. The freedom to choose arbitrary
impedance levels provides advantages in that circuits can drive or be driven by
an impedance that best suits them. On the other hand, if circuits are connected
using transmission lines, then these circuits are usually designed to have an
input and output impedance that match the characteristic impedance of the
transmission line.
Re: difference between analog and rfic
Signal, noise, and distortion levels are also described differently in low frequency
analog versus microwave design. In microwave circuits, power is usually used
to describe signals, noise, or distortion with the typical unit of measure being
decibels above 1 milliwatt (dBm). However, in analog circuits, since infinite or
zero impedance is allowed, power levels are meaningless, so voltages and current
are usually chosen to describe the signal levels. Voltage and current are expressed
as peak, peak-to-peak, or root-mean-square (rms). Power in dBm, PdBm, can be
related to the power in watts
Re: difference between analog and rfic
Similarly, noise in analog signals is often defined in terms of volts or
amperes, while in microwave it will be in terms of dBm. Noise is usually
represented as noise density per hertz of bandwidth. In analog circuits, noise
is specified as squared volts per hertz, or volts per square root of hertz. In
microwave circuits, the usual measure of noise is dBm/Hz or noise figure, which
is defined as the reduction in signal-to-noise ratio caused by the addition of
the noise.
In both analog and microwave circuits, an effect of nonlinearity is the
appearance of harmonic distortion or intermodulation distortion, often at new
frequencies. In low-frequency analog circuits, this is often described by the ratio
of the distortion components compared to the fundamental components. In
microwave circuits, the tendency is to describe distortion by gain compression
(power level where the gain is reduced due to nonlinearity) or third-order
intercept point (IP3).