Evaluation Board Hardware; Power Supplies; Guard Ring Features; Frequency Response - Analog Devices EVAL-ADA4350RUZ-P User Manual

EVAL-ADA4350RUZ-P User Guide

EVALUATION BOARD HARDWARE

POWER SUPPLIES

The ADA4350 has two supplies. The analog supply is used to
power up all the analog circuitries while the digital supply is
used to power up all the digital controls. The two supplies
have separate grounds inside the chip. Table 1 shows the
supply range of the analog and digital supply, the voltages to be
applied to the supply pins in different configurations, and their
limitations.

GUARD RING FEATURES

The ADA4350 evaluation board employs a two layer
electrostatic guarding to minimize leakage currents from
entering the TIA node.
Five mil wide guard rings encircle the inverting and
noninverting input components on the top copper layer (see
Figure 7 and Figure 9). The guard rings connect to the internal
GND copper layer with 5 mil dia vias. Each component pad
that connects to the TIA inverting and noninverting inputs is
connected to an internal copper trace with 5 mil dia vias (see
Figure 8 and Figure 9).
This electrostatic guarding scheme provides isolation from
leakage currents but adds a 35 pF parasitic capacitance to the
TIA inverting node.

FREQUENCY RESPONSE

The ADA4350 evaluation board is configured for a simulated
photodiode input. The photodiode capacitance is represented
by C1, a 51 pF capacitor. The photodiode current is simulated
by the input voltage Vin-N and R2, a 100 kΩ resistor. I
= (Vin-N)/100 kΩ.
The total capacitance (91 pF) seen by the TIA is the sum of the
ADA4350 input capacitances (2 pF + 3 pF), the photodiode
capacitance (51 pF), and the parasitic capacitance of the
electrostatic guarding (35 pF).
Table 1. Powering Up the Analog and Digital Supplies
Supply Supply Range (V)
Analog 3.3 to 12
Digital 3.3 to 5.5
The five feedback resistor values are approximately ½ decade
apart. The five compensation capacitors are selected for
maximum bandwidth and maximum gain flatness.
The normalized transimpedance and noise gain are shown in
Figure 3 and Figure 4 with compensation capacitors installed
and not installed.
1000k
100k
10k
1k
0.1k
0.01k
Figure 3.
50
40
30
20
10
PHOTODIODE
0
–10
–20
–30
0.1M
Figure 4.
Dual Supplies (±V )
S
VCC GND
+V 0
S
VCC to DGND
≥3 V
Rev. 0 | Page 3 of 8
= 1kΩ
R
F
= 3kΩ
R
F
= 10kΩ
R
F
= 30kΩ
R
F
= 100kΩ
R
F
0.1M 1M 10M
FREQUENCY (Hz)
ADA4350 Signal Gain and Noise Gain Frequency Response
= 1kΩ, C
R = 15pF
F F
= 3kΩ, C
R = 6.8pF
F F
= 10kΩ, C
R = 3.3pF
F F
= 30kΩ, C
R = 2.2pF
F F
= 100kΩ, C
R = 1pF
F F
1M 10M
FREQUENCY (Hz)
ADA4350 Signal Gain and Noise Gain Frequency Response
Single Supplies (+V
VEE VCC
−V +V
S S
VCC to DGND
UG-655
= 1kΩ, C
R = 15pF
F F
= 3kΩ, C
R = 6.8pF
F F
= 10kΩ, C
R = 3.3pF
F F
= 30kΩ, C
R = 2.2pF
F F
= 100kΩ, C
R = 1pF
F F
100M
= 1kΩ
R
F
= 3kΩ
R
F
= 10kΩ
R
F
= 30kΩ
R
F
= 100kΩ
R
F
100M
)
S
GND VEE
0 0
≥3 V