I am using an AD8302 RF/IF Gain Phase detector to measure the gain and phase of two input signals within a varying frequency range of 1Hz to 1MHz. It is mentioned in the application note AN-691 that the IC need to be used in the following configuration to enable its use in low frequency applications:
I gave a +5V supply to the IC and used CC = 10uF ,CFLT = 1uF. Also R1= R2 was chosen as 51.9 Ohm.
The input signals were VINA = VF1 and VINB =VF2 as shown in the following circuit:
As per the datasheet of AD8302,the gain and phase measurements are related to the voltage outputs as:
where VCP =900 mV,RFISLP = 600 mV/decade and RFIQ = 10mV/degree at low frequencies.
I acquired a Bode plot of the same circuit using the Bode analyser of NI ELVIS II+ and also obtained the Gain in dB and Phase in degrees using the above equations from the AD8302 output voltages.
The measurements are graphically represented as below: