T3 Mixer Primer: A Mixer for the 21st Century
Section 1. T3 Mixer Overview
The T3 mixer possesses the following properties:
1. Low conversion loss and extremely wide bandwidth. Typical conversion loss is 7 dB with a bandwidth of 10 MHz to 12 GHz.
2. Unparalleled IMD suppression. Input third order intercept (IIP3) performance is typically 10 dB higher than the LO drive across the band. IIP3 values as high as 20 dB above the LO drive have been witnessed in lab.
3. High 1 dB compression point. The T3 compression point is approximately 1‐3 dB below the LO drive level. Conventional mixers compress 5‐7 dB below the LO drive level.
4. LO drive level flexibility. A T3 mixer’s conversion loss is constant for LO drives ranging from +12 dBm through +25 dBm. As LO drive increases, 1 dB compression and IMD performance improve nearly dB for dB. No other mixer exhibits this unique property.
5. T3 mixer performance optimizes with a square‐wave LO drive.
Two key breakthroughs enable the T3 mixer: the use of near‐ideal commutating behavior and the employment of internal feedback circuitry. It has been known for over half a century that commutating (i.e. switching) mixers produce ideal IMD behavior. In switching mixers, the unwanted nonlinear characteristics of the diode are minimized such that only the LO is capable of turning the diode ON and OFF. When combined with square‐wave LO drive, the linearity of the commutating mixer is additionally improved because the switching is allowed to occur nearly instantaneously. The T3, as it will be demonstrated, combines switching behavior and square‐wave drive to achieve unparalleled linear performance.