The balun of nrf51822

[KING JAMES]

I simulated the balun of nrf51822 accroding to the referenced design of nrf51822 on the official website.
However,it showed the differential phase of the balun was not 180 degrees.
Please help me to find a solution,thanks.

[KING JAMES]

[ketiljo]

When you simulate the phase difference on the pins, you will find that this is not 180 degrees. Inside the radio front end, on the PA output in TX mode and on the input of the LNA in RX mode, you will find that the phase difference is close to 180 degrees. 

[KING JAMES]

What is the output impedance of the nrf51822 Radio Frequency output port?

[ketiljo]

The optimal load impedance is 15 +j85 ohm. This is not the reciprocal of the output impedance,  but the load impedance that gives the highest output power and lowest noise in the RX LNA.

[KING JAMES]

1.Please tell me the specific description in official document about the impedance of the Nrf51822 RF port and the design of the Balun circuit.

2.When simulating the circuit with ADS,how should the impedance of two RF ports be set respectively？

[ketiljo]

1. See the product specification, chapter 8.5.7

2. The impedance in #1 is what the radio will like to see, yes, not 50 ohm

Note that you're missing the properties of the PCB, like tracks, pads etc, so your results may not be very accurate.

[KING JAMES]

1.Is the theoretical impedance of point A to the ground 50 ohms?

2.I simulated the circuit diagram above and found that the impedance was 28+j*51, not 15+j85.

Is this simulation circuit correct?

If the layout simulation with PCB, can we get 15+j*85 and NRF can work properly?