www.ti.com
Vin
THS4503
AINP
AINN
47 pF
787
W
+VCC
0.1 F
m
10 F
m
10 F
m
0.1 F
m
12
W
100 pF
12
W
100 pF
100 pF
787
W
-VCC
374
W
402
W
56.2
W
Vocm
+2.5 V
47 pF
2.1.2
External Reference Generation
Introduction
The ADS1610 has relaxed antialiasing filter requirements because it is a delta sigma converter. A simple
antialiasing filter comprising a 24-
Ω
resistor and a 300- pF capacitor with a –3-dB bandwidth of 22 MHz is
used at the output of the THS4503.
Figure 1. Input Circuitry
The ADS1610 operates from an external voltage reference. The reference voltage VREF is set by the
differential voltage between VREFN and VREFP: VREF = (VREFP-VREFN). VMID must be 2.5 V.
The ADS1610EVM has onboard reference generation circuitry using the low-noise, high-speed THS4031
from Texas Instruments. Three of these amplifiers are used to generate the REFP (VREFP), CML (VMID)
and REFM (VREFM) voltages. The CML voltage generated in this circuitry also is used as the
common-mode voltage for the input driver (THS4503). The three reference voltages can be adjusted using
the trim potentiometers R37, R38, and R40.
The reference voltage source for the onboard reference generation circuitry is selectable. If W1 jumper
position is across pins 1 and 2, then AVDD1 is selected. When the jumper is placed across pins 2 and 3,
the REF02 is selected as the source. The ADS1610EVM leaves the factory with a short across pins 2 and
3 of W1.
The factory-set voltages are 4 V, 2.5 V, and 1 V for VREFP, VCML, and VREFM, respectively. These
voltages provide a reference voltage of 3 V single-ended. The ADS1610 with a 3-V reference can achieve
an SNR of 86 dBFS in the 0 – 5-MHz bandwidth.
If the application requires a smaller reference voltage, then potentiometers R37 and R38 can be adjusted
to generate the desired voltage. Be aware that there is a tradeoff between SNR and reference voltages.
gives the reference voltage versus SNR tradeoff.
Table 1. Reference Voltages
Reference
VREFM
VCML
VREFP
Peak In-Band SNR
3 V
1
2.5
4
86
2.5 V
1.25
2.5
3.75
85
2 V
1.5
2.5
3.5
83
SLAU180A – May 2006 – Revised August 2006
ADS1610EVM
3
