Low power direct conversion I/Q modulator has better than 50dB sideband & carrier suppression

The LTC5599 is a direct conversion I/Q modulator designed for low power wireless applications that enable direct modulation of differential baseband I and Q signals on an RF carrier. Single side-band modulation or side-band suppressed upconversion can be achieved by applying 90° phase-shifted signals to the I and Q inputs. The I/Q baseband input ports can be either AC or DC coupled to a source with a common mode voltage level of about 1.4V.

This low power I/Q modulator from Linear Technology enables battery-powered transmitters operating in the 30MHz to 1.3GHz frequency bands, breaking new ground in power consumption, sideband suppression, carrier leakage and dynamic range performance. The 92mW  LTC5599 modulator, powered from a single 2.7V to 3.6V supply, draws only 28mA current, less than 60% that of alternative solutions – with no performance sacrifice.

The LTC5599 delivers outstanding native -52.6dBc sideband suppression and -51.5dBm carrier leakage without calibration. With on-chip calibration resources, performance can be further improved to -60dBc and -65dBm, respectively. Moreover the device output achieves an excellent noise floor of -156dBm/Hz with an OIP3 of 20.8dBm, delivering superior transmitter performance.

This device combines low power consumption and robust performance to suit a wide range of demanding battery-powered radios and wireless communications applications that are exposed to strong radio interference. These include wireless professional microphones, frequency hopping narrowband and broadband portable field radios, public safety radios, train communications, as well as broadband VHF/UHF white space modems, software-defined radios, portable RF test equipment, picocell base stations, low-power microwave backhaul, small wireless repeaters and satellite modems.

The gain of this device can be set via the on-chip serial port. A coarse gain control provides 1dB/step, along with adjustable fine gain control of 0.1dB. Total gain ranges from -19dB to 0dB. Varying the modulator gain enables device supply current from 8mA to 35mA, allowing the device to be set to lower power consumption with slightly reduced gain and performance, as needed for specific applications. Once set, the gain can be automatically temperature compensated by activating the on-chip temperature correction feature.

The SPI interface controls the supply current, modulator gain, and allows optimization of the LO carrier feedthrough and side-band suppression, with sine wave or square wave LO drive. A fixed LC network on the LO and RF ports covers a continuous 90MHz to 1300MHz operation. An on-chip thermometer can be activated to compensate for gain-temperature variations. More accurate temperature measurements can be made using an on-chip diode. In addition, a continuous analog gain control (V_CTRL) pin can be used for fast power control.

The LTC5599 supports narrowband and wideband radio applications. It’s I and Q inputs are each capable of -1dB modulation bandwidth of up to 37MHz, supporting a total of 74MHz RF bandwidth at 900MHz frequency.

The LTC5599 is available in a 4mm x 4mm QFN package, providing a compact footprint. The product is specified for case operating temperature from -40°C to 105°C, supporting reliable operation in extended temperature environments. The device can be conveniently shut down with an enable control pin. When disabled, the device conserves power by drawing a typical of 0.7µA standby current. The LTC5599, priced starting at $4.45 each in 1,000-pieces quantities, is available in production quantities.

The USA list pricing shown is for budgetary use only. International prices may differ due to local duties, taxes, fees and exchange rates.

For more information, visit www.linear.com/product/LTC5599

Summary of Features of the LTC5599:

• Operating Frequency          30MHz to 1.3GHz
• Power Consumption           3.3V / 28mA
• Sideband Suppression       –52.6dBc at 500MHz
• Carrier Leakage                  –51.5dBm at 500MHz
• Output IP3                                       +20.8dBm
• Output IP2                                       +63.6dBm
• Output Noise Floor             –156dBc/Hz at P_OUT = 3dBm
• SPI Serial Bus Control:
  • Adjustable Gain: –19dB to 0dB in 1dB Steps
  • Gain Changes Affect Supply Current from 8mA to 35mA
  • I/Q Gain/Phase Adjust: Up to –60dBc Sideband Suppression
  • I/Q Offset Adjust:  Up to –65dBm Carrier Leakage