4 Application: ADC Channel Summation to Improve TAC5212 Dynamic Range

Consider two inputs, which have a signal component, and a noise component.

When these two inputs are mixed together, the signal component is correlated, and hence adds directly, whereas the noise component is uncorrelated, and adds as root-sum-square.

Therefore, when the two inputs are mixed together in equal weight, the resultant output is:

If the same source is used for both inputs (as shown in Figure 4-1), then:

The resulting output is

While the signal amplitude remains the same, the noise has reduced by a factor of 1.414. This can result in an improvement in the signal-to-noise ratio of the effective output by 3dB

This concept was tested out in TAC5212EVM-K, with the following configuration script and the same analog signal connected across both IN1P/M and IN2P/M.

w a0 00 00 # Page 0 
w a0 01 01 #SW Reset
d 01

# Page 0 Register Writes
w a0 00 00
w a0 02 09 #Exit Sleep Mode with DREG and VREF Enabled
d 10
w a0 1a 30 #PASI in TDM protocol with 32-bit word length
w a0 4d 00 #VREF set to 2.75V for 2Vrms differential fullscale input
w a0 50 00 #ADC Channel 1 configured for AC-coupled differential input with 5kOhm input impedance and audio bandwidth
w a0 55 00 #ADC Channel 2 configured for AC-coupled differential input with 5kOhm input impedance and audio bandwidth


w a0 1e 20 #Recording Channel 1 on TDM Slot 0
w a0 1f 21 #Recording Channel 2 on TDM Slot 0


#Same signal on ADC CH1, ADC CH2
w a0 00 0a #Page 10
#Confugre Mixer1 for OUT1 = 0.5*IN1 + 0.5*IN2
w a0 08 40 00 00 00
w a0 0c 40 00 00 00
w a0 10 00 00 00 00
w a0 14 00 00 00 00
#Confugre Mixer1 for OUT2 = 0.5*IN1 + 0.5*IN2
w a0 18 40 00 00 00
w a0 1c 40 00 00 00
w a0 20 00 00 00 00
w a0 24 00 00 00 00


w a0 00 00 #Page 0
w a0 76 c0 #ADC Channels 1-2 Enabled
w a0 78 80 #ADC Powered Up

Table 4-1 shows the dynamic range with CH1 and CH2 individually, along with the 3dB improvement seen through channel summation. The measurements are A-weighted.