RF ICs for radio amateurs 2 Mixers
Basics and where to find them • http://www.minicircuits.com/appnote/mixer1-2.htm • Covers intercept point (IP3), conversion loss, isolation, VSWR, 2-tone 3rd order IMD – and how to measure them • Also for background on the “classic” NE602 : • http://www.electronics-tutorials.com/devices/602.htm • and download • http://www.semiconductors.philips.com/acrobat_download/applicationnotes/AN1981.pdf
Mixer aka modulator • NB : a multiplier is a type of mixer
Mixer types / configurations • Unbalanced mixer – no port-to-port isolation • (LO and input also appear at output) • Single balanced mixer • cancels 1 i/p at output, usually the RF i/p. • 2 SBMs can be phased to cancel both RF & LO • Double Balanced Mixer • can phase 2 of these to cancel a mixing output i.e. SSB mixer. • Commutating or not • (squarewave or sine LO) ? • Square gives less conversion loss and noise. • Sine gives fewer Sq. wave harmonic issues.
Gilbert Cell Multiplier- Barrie Gilbert, a Brit ! • Gilbert • In 1968, Barrie Gilbert published a paper on a four quadrant analog multiplier which combined the circuit of the Jones patent along with predistortion circuitry to make a large signal four quadrant multiplier. The entire content of the paper was about accuracy of multiplier circuits used in analog computers. In 1974 a further paper was published showing how to reduce the multiplication errors even further. It was the integrated nature of the circuitry that made the transistors match which made the circuit accurate. No reference was made to radio mixers in either paper. The circuit The Jones patent was referenced. • Gilbert cites the Jones patent in his first paper. He, like tens of thousands of engineers in the previous 15 years, had independently conceived of using bipolar transistors in the topology that had previously used vacuum tubes. • Gilbert is currently active in trying to improve all transistor mixers.
DC to 2.4 Ghz • AD831 • old, bomb proof, widely used in amateur radio • AD8342 • modern, tiny 3x3 mm package • AD8343 • works down to DC , but IP3 only +16.5 dBm. • Lower LO drive requirement, 5 x 4.5 mm • AD8344 • rx optimised, SiGe, 3mm x 3mm package • ADL5350 • to 4 GHz. 6dB NF, tiny package • ADL5390 • to 2.4 GHz, 2 input vector multiplier , • specialist IC with 2 mixers using linear multipliers.
How to solder SMDs • Many good refs in Radcom and on web • http://www.piclist.com/techref/smds.htm • http://www.geocities.com/vk3em/smtguide/websmt.html (VK3EM) • http://www.tutorialsweb.com/smt/chapter7c.htm#7.3 • and many more
AD831 – used by many radio amateurs • RFP and RFN, and the LOP and LON, inputs are symmetrical. • IF out can be SE or differential • (op-amp used or not) • AD831 is a balanced modulator • (not a linear multiplier) • The RF input drives a linear signal to the mixer core • LO input feeds a limiting amplifier which switches hard with a 200mV pk-pk signal • The 831 has output op amps that can be used for gain • +20 dB achievable.
AD8343 • More recent IC than AD831 • Similar performance but works to 2.5 GHz • Can work off 2.7 V supply • Wideband, so we only had time to test it at some key frequencies dictated by our main target markets and by some our lead (high volume) customers. • 20 uA powerdown mode • Interesting Evaluation Board – 2 x AD8343 with separate sections.
AD8344 • 3 x 3 mm package • SiGe process • SE (unbalanced) RF and LO ports • Powerdown pin – does this in <1 uSecond • Intended for down conversion • high side LO • The conversion gain of the AD8344 decreases with increasing frequency. • By choosing a high side LO, the intended RF signal at fLO - fIF is frequency translated with greater gain than the image at fLO + fIF. • Using a low-side LO, the image noise would have greater impact on noise figure.
AD8344 -continued • Pin compatible with AD8342 (another 3 x 3 mm mixer) • AD8342 = 50-500 MHz RF in (LO 60-850) • AD8344 = 400 MHz-1.2 GHz (LO 470-1600)
ADL5390 • Not really a “mixer” • Basically two multiplying VGAs in single IC that are combined at the output. • Linear multipliers used in the VGAs • Can complement AD8302 2 channel gain/phase detector • Can do AM modulation • (tie I and Q control signals together and apply modulating wave to them)