In this report, I describe tests of two quadrature mixer ICs as candidates for use in the digitizer module, where they would convert the 1-2 GHz IF to in-phase and quadrature baseband signals which would in turn drive two analog-to-digital converters.
Quadrature mixers, or I/Q mixers, are available as integrated circuits from many manufacturers. Most are designed for UHF input signals (300-500 MHz), but there are also several that work up to or slightly beyond 2 GHz. Nearly all of them have per-channel output bandwidths around 30 MHz or less, which is too small for our purposes. The two tested here, the Maxim MAX2108 and the Analog Devices AD8347, are exceptions in that they have output bandwidths of more than 50 MHz while covering the input range 1-2 GHz. The MAX2108 has the largest baseband range of all such ICs that I have found, namely 0-150 MHz (at -3 dB). (Note that in our application the IF bandwidth is twice the maximum baseband frequency.) However, neither device's data sheet contains useful specifications on its accuracy; each claims less than 3 deg phase error and good amplitude match, but only at a very low output frequency, with no information about performance over the whole useful bandwidth. Telephone inquiries to the manufacturers produced disclaimers of any knowledge of the broadband accuracy. Consequently, the tests reported here were undertaken.
In this report, I describe tests of two quadrature mixer ICs as candidates for use in the digitizer module, where they would convert the 1-2 GHz IF to in-phase and quadrature baseband signals which would in turn drive two analog-to-digital converters.
Quadrature mixers, or I/Q mixers, are available as integrated circuits from many manufacturers. Most are designed for UHF input signals (300-500 MHz), but there are also several that work up to or slightly beyond 2 GHz. Nearly all of them have per-channel output bandwidths around 30 MHz or less, which is too small for our purposes. The two tested here, the Maxim MAX2108 and the Analog Devices AD8347, are exceptions in that they have output bandwidths of more than 50 MHz while covering the input range 1-2 GHz. The MAX2108 has the largest baseband range of all such ICs that I have found, namely 0-150 MHz (at -3 dB). (Note that in our application the IF bandwidth is twice the maximum baseband frequency.) However, neither device's data sheet contains useful specifications on its accuracy; each claims less than 3 deg phase error and good amplitude match, but only at a very low output frequency, with no information about performance over the whole useful bandwidth. Telephone inquiries to the manufacturers produced disclaimers of any knowledge of the broadband accuracy. Consequently, the tests reported here were undertaken.