SIGNAL PROCESSING COMPONENTS DEFINITIONS

MIXERS

ETTI's double-balanced mixers are usually used to convert a signal from one frequency to another.  The mixer is driven by a Local Oscillator (LO) and the signal to be converted is the Linear Signal.  A mixer will have two outputs - an upper sideband (LO plus the Linear signal) and a lower sideband (LO minus the linear signal).  For example, with a 10 MHz LO signal and a 1 MHz Linear signal, the two outputs would be 9 MHz and 11 MHz.  The desired signal is selected and the other filtered out.  A special type of mixer that has only one input can be used to double a frequency.  Our mixers are passive, that is, they do not require a DC power source.

The LO signal is used to switch the diodes in the mixer and must be high enough to thoroughly do so.  The diodes chosen in the design of the mixer are determined by the LO level desired.  A LO drive level can be from +7 dbm to +32 dbm and is determined by the maximum signal level of the Linear signal.  For +7 mixer, the linear signal can be up to -3 dbm level.  For a +17 dbm mixer, the linear signal can be up to +10 dbm.  Normally, the maximum Linear signal would be about 10 db below the LO level.

Conversion loss is the difference between the level of the linear signal coming into the mixer and the level of the desired sideband coming out of the mixer.  this loss can be as low as 6 db.

Our mixers are double-balanced - that is, both the LO and the Linear signal are balanced out and show up at a greatly reduced level in the output.  This is known as isolation and is a part of the mixer's specifications.

Mixers can be used anytime a signal is needed to be converted to another frequency.  Applications include; transmitters and receivers, test equipment, environmental monitors and any type of data stream using a RF signal as the carrier wave.

FREQUENCY DOUBLERS

ETTI miniature printed circuit board mountable frequency doublers provide a simple and inexpensive way to double any frequency in the 500 kHz to 1000 MHz range, in addition to doubling the frequency, they will provide considerable rejection of the input fundamental frequency and its higher harmonics.

SWITCHES

ETTI's radio frequency switches are transformer driven diode switching networks.  They are very fast (on the order of 2 nanoseconds) and have excellent on/off ratios.  A plus and minus DC current of 20 milliamps is required to switch the diodes.  The diodes used in ETTI's switches are very high-speed hot-carrier diode quads.

Frequency ranges of this type switch are usually limited to 500 MHz.  Special switches using pin diodes are available for higher ranges.  Our switches are 50 ohm impedance when turned on and special models are available to maintain a 50 ohm impedance in both on and off configuration.

Applications are where a high speed RF signal switch is needed.

POWER DIVIDERS/HYBRIDS

Power dividers are what the name implies - a device to divide a signal into two or more parts.  They may also be used as combiners since they are fully bi-directional.  The outputs may have an amplitude or phase relationship and will usually cover a specific frequency range.

An in-phase divider will have outputs that have a 0 degree relationship to each other and have the same amplitude.  A 180 degree divider has equal amplitude outputs but they will be 180 degrees apart in phase.  A device known as a Magic-T will have both in-phase and 180 degree outputs.

A 90 degree or quadrature divider will have outputs that are 90 degrees apart with the same amplitudes over a specific frequency range.  The range is usually limited to a 2:1 maximum ratio.  A narrow-band divider will usually cover a specific frequency but can be used over a 10% bandwidth quite well.

In-phase power dividers are available for 2-way up through 32-way.  Impedances are available for both 50 ohm and 75 ohm.  Maximum signal level is typically +20 dbm but higher power levels can be handled with special considerations.  Dividers able to handle high power will require that any unused inputs/outputs be terminated into a suitable load to properly dissipate the energy outside of the unit.

Power dividers can be used anywhere a signal needs to be divided or multiple signals combined.  Such as;  multiple devices that require the same signal input, splitting a signal for feeding many antennas or splitting a signal for use in a feedback system.  Typically, combiners are used to integrate multiple signals into one signal stream, combining the outputs of several amplifiers before feeding the signal to an antennae or, as in the case of a cell phone system, combining many phone calls into one transmitted signal.

TRANSFORMERS

Transformers are used as impedance or phase transformation devices, for isolating circuits or for both.  They can be single-ended to balanced or any combination desired.  Frequency ranges up to 2 GHz are available.  Either inputs or outputs may be center-tapped.

The simplest is known as an auto transformer and is used only for impedance transformation.  An example would be 50 ohms to 100 ohms with a common ground between input and output.  These usually work well over a wide frequency range and are simpler and thus less expensive.  Auto transformers do not have DC isolation.

A phase reversal or shifting it 180 degrees is done with a simple co-axial transformer using a primary and secondary.

A balanced output transformer will have a center-tapped secondary and may have a balanced or un-balanced input.

Impedance transformers usually will have inputs of 50 or 75 ohms which is then matched to a higher or lower impedance.  Normally, a very high ratio (such as 50 to 800 ohms) will have a limited frequency range due to inter-winding capacitance.

ETTI uses special winding techniques to provide good balance and low insertion loss in our transformers.  In general, our transformers are low power (less than +20 dBm)  but special transformers for high power are available.

Typical uses include matching impedances as in the case of a typical radio signal operating at 50 ohms but feeding a television cable that operates at 75 ohms.  Electrically isolating circuits from each other but still allowing a signal to pass through is another possible application.  Phase reversal can be used in directional antennas and canceling out unwanted signals.

PHASE SHIFTERS

Phase shifters are designed to shift the output phase of a signal with respect to the input.  These can either be mechanical or electrical.  They are very frequency dependent such that a setting at a particular frequency will change as the incoming signal is changed.

Frequency ranges are available up to about 1 GHz with amplitude levels up to +10 dBm.  Bandwidths of 10% is a limitation imposed by design considerations.  Control voltages for the phase shift run between 1 and 10 volts.  These are not linear devices, the control voltage vs. phase shift curve is in the shape of an S.  Devices with 180 degree or 360 degree total shift are available.

Delay lines are a specific type of phase shifter and are used for a fixed phase shift at a specific frequency.

Phase shifters have a variety of practical applications;  narrow beam directional antennas, test setups for RF devices, measurement of circuit paths and  compensation for cable or circuit length

COUPLERS

Couplers are designed to take a small portion of the signal passing through the device and feed it off to an external circuit for measurement or control purposes.  A typical coupler would have a coupled output of 10 or 20 db.  This means that the coupled output is 10 or 20 db below the main signal passing through it.  The other port, the null port, can be used to tune a matching network when impedance matching is desired.

The directivity of a coupler is a measure of how well the coupler is designed and is measured at the null port.  A very low value at the null port means that all impedance are matched and the coupler is low loss.

Special couplers of other db values can be designed, if desired.  We have couplers of 6 db to more the 20 db available.

Applications include;  signal sampling, closed loop feedback systems, antennae tuning networks and non-symmetrical power dividers.

IQ NETWORKS

I and Q modulators/demodulators are a combination of two mixers, a 90 degree power divider and an in-phase divider.  These are used to generate two signals (mixed up or down) that are 90 degrees apart.

They can be used as phase detectors, modulators (both phase and amplitude) phase comparators and SSB (Single Side Band) modulators.

Frequency limitations are imposed by the frequency range of the 90 degree power divider.  This could be over a 2:1 frequency range or a slightly simpler one can be designed if the bandwidth is 10% of less.  LO drive level requirement are the same as for mixers except for an additional 3 db required since we drive two mixers from one source.  Isolation is also dependent on the construction and balance of the mixers and power dividers.

A special application for the IQ network is an Image Reject Mixer.  In this case, two 90 degree dividers are used and one output will have a suppressed upper sideband and the other will have a suppressed lower sideband.  This allows a signal to be used with less filtering of the unwanted harmonics.

When used as a phase detector, the IQ Network will give 20 outputs that can be used to determine the phase difference between 2 separate signals.  The outputs are dc voltages that are proportional to the sine and the cosine of the phase difference between the signals.  This information can in turn be used to determine the direction of a signal source from the receiving antennas.

When used as a modulator, a data or voice signal can be imposed on a carrier wave.  This is the manner that AM radio uses to put a voice/music signal onto its high frequency carrier wave.  Conversely a demodulator does the opposite.  It removes a signal from its carrier wave.

OTHER COMPONENTS

ETTI also produces directional couplers that operate from 500 kHz to 1 GHz with coupling ratios from 6 dB to 20 dB, voltage variable attenuators, delay lines, bi-phase modulators, and phase detectors in miniature leaded and surface mount packages.