Solution: Mixer output noise with ADL5802 Demo Board - varying Supply Current

Original Question: Solution: Mixer output noise with ADL5802 Demo Board - varying Supply Current by Jan_V We found a problem with our ADL5802 Demo Board, showing high levels of output noise on Mixer output. This board was purchased direct from AD. We also noticed fluctuating Bias Current from 130mA to 150mA with Vset=2V and raised Case #: 2E15LU04568. Subsequently we found that flexing the board and pressing down the ADL5802 chip seems to indicate a hardware problem with the board with poor connection or soldering joint suspected. Solution: As the demo board was no longer in warranty, we resoldered all components on the board. We then found there was no connection between the VPOS board pin and chip pins that should see supply voltage. As the supply lines run on inner layers which are not documented by AD, we soldered a wire from the board pin to one of the points where we knew the supply voltage should go. Now, the mixer current is back and rock stable at 160mA for Vset=2V. Also the mixer output level is now constant. No more flexing or pressure sensitivity. We believe the issue was caused by an poor connection in one of the inner layer tracks on the ADL5802 Demo board. This information is posted for the benefit of other users of this board. a) Mixer Output noise as found on first use at 100 MHz Mixer Output. Note Y scale is 0.01 dB/Div is correct. Ref1 indication is with attenuation applied. The RF source at 100MHz delivers a ‐13dBm sinewave signal to the mixer RF1 input port. The LO source at 110.7MHz delivers a 2dBm rectangle signal to the mixer LO port. Mixer output is at 10.7 MHz. Screenshots taken with DG8SAQ Vector Network Analyzer. b) Mixer output noise as found after repair of the ADL5802 Demo board. Mixer output is clean and Current consumption is rock steady at 160mA Again note Y scale resolution 0.01 dB This information is posted for the benefit of other users of this board.

ADL5802 Low Frequency Operation

Q. The ADL5802 datasheet states that the device is capable of operation to frequencies as low as 100 MHz, yet the Typical Performance Characteristics plots only show data as low as 500 MHz. Is the device capable of operation at these low frequencies and is there any typical performance data available? ---------------------------------------------------------------------------------------------------------------------- A. The ADL5802 is indeed capable of operating at frequencies as low as 100 MHz and below. In order to achieve low frequency operation some changes are necessary to the standard evaluation board. Specifically, the RF series input capacitors (C5, C12, C13 & C14) should be changed from their datasheet recommended value of 100pF to a higher value of 1nF. The lower capacitor values create a highpass filter effect on the input resulting in poor return loss at low frequency which should be avoided. The performance of the ADL5802 was characterized for IF frequencies of 10 MHz and 70 MHz in Low Side LO and High Side LO configurations. The typical performance of the ADL5802 can be seen in the attached plots. The standard ADL5802 evaluation board configuration was used. Capacitors C5, C12, C13 & C14 were replaced with 1nF capacitors. VS=5V, VSET=3.8V, unless otherwise noted. The 4:1 IF port transformer (TC4-1W+), the RF and LO port transformers ( TC1-1-13M+) and PCB loss are included in the measurement. Summary: The ADL5802 under low frequencies indicates the following typical performance: Gain = 0.6dB (Balun and PCB loss inclusive), IIP3 = 33dBm, IIP2 = 70dBm, P1dB = 13dBm and Noise Figure = 11dB. Attachments: ADL5802_Low_Frequency_operation_Summary.pdf