What is the minimum bias voltage at the IF outputs of the LTC5510 to ensure normal operation and avoid significant performance degradation when using pull-up resistors with a 5V supply?

The datasheet does not provide explicit guidance on the minimum bias voltage for the IF outputs when using pull-up resistors. However, based on the gain and IP1dB specifications, the output voltage swing at 900 MHz is 2.7V pp, which means the output voltage swings from (5V+1.35V) to (5V-1.35V) with a 5V supply and bias inductors. The lowest voltage seen at the output is 3.65V. To ensure normal operation, it is recommended to set the bias level at around 4V, allowing an output swing of +/-0.35V, or 0.9dBm. Using a 50 ohm pull-up resistor with a 5V supply results in a bias voltage of 3.4V, which is close to the minimum acceptable level. However, caution is advised when reducing the bias voltage further, as it may affect the performance or operation of the LTC5510.

What is the purpose of the 0.05 pF component between the IN+ and IN– pins of the LTC5510 mixer.

Answer: The 0.05 pF capacitor improves matching at higher frequencies; the datasheet specifies its use up to 6 GHz. Comparing the input return loss for that matching topology with the circuit on page 25 of the datasheet , shows a much narrower response illustrateing its effect.