Current-to-Voltage Converter Circuit for Audio DACs

Rajkumar Sharma
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SKU: EL156716
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Many high-performance audio digital-to-analog converters (DACs) feature a current output that must be converted into a voltage output for use with audio amplifiers. In premium automotive audio applications, for example, it is critical that the DAC signal-to-noise ratio (SNR) and total harmonic distortion plus noise (THD+N) performance is not compromised by the current-to-voltage (I-V) output stage. The first stage of the circuit converts the current output to a voltage output by providing a virtual ground potential to the OUTP and OUTN nodes of the DAC. The current flowing from the DAC then creates a voltage across the resistor, R4, R18, in the feedback loop. Note that current-output audio DACs have a common mode current that creates an offset to confirm that the DAC is always sourcing current. This common-mode current also results in the output of the first stage always being a negative value. The supplies of the amplifiers of the circuit are not required to be symmetrical. The second stage of the circuit is a differential amplifier that converts the differential voltage of the first stage into a single-ended output voltage. In the third-order, low-pass filter (LPF) circuit, the output level of 2.1 V RMS and 123-dB signal-to noise ratio is achieved. A NE5534 operational amplifier is used for the I/V circuit to obtain the specified performance. Dynamic performance such as the gain bandwidth, settling time, and slew rate of the operational amplifier affects the audio dynamic performance of the I/V section. The current of the PCM1795 device on each of the output pins (IOUTL+, IOUTL–, IOUTR+, IOUTR–) is 4 mA-PP at 0 dB (full-scale).

The project is compatible with our Stereo Audio Digital-to-Analog Converter Module

Circuit Credits: Circuit ideas taken from Texas Instruments PCM1795 IC Datasheet.

Features

Power Input +/-15V DC (Dual 15V DC)
On Board Power LED
Stereo Output Signal 2.1V RMS
Header Connector for Input Signals
Screw Terminals for Audio Output
PCB Dimensions 46.99 x 33.66 mm

Connections

CN1 Signal Inputs: Pin 1 = L-Channel -In, Pin 2 = L-Channel +In, Pin 3 = R-Channel -In, Pin 4 = R-Channel +In, Pin 5 = GND
CN2 Power Input: Pin 1 = +VCC, Pin 2 = GND, Pin 3 = -VEE
CN3 Signal Output: Pin 1 = Left Channel Output, Pin 2 = GND
CN4 Signal Output: Pin 1 = Right Channel Output, Pin 2 = GND
D1: Power LED

Schematic

Parts List

NO	QNTY	REF.	DESC	MANUFACTURER	SUPPLIER	SUPPLIER PART NO
1	1	CN1	5 PIN MALE HEADER PITCH 2.54MM	WURTH	DIGIKEY	732-5318-ND
2	1	CN2	3 PIN MALE HEADER PITCH 2.54MM	WURTH	DIGIKEY	732-5316-ND
3	2	CN3,CN4	2 PIN SCREW TERMINAL PITCH 5.08MM	PHOENIX	DIGIKEY	277-1247-ND
4	14	C1,C2,C3,C4,C5,C6,C7,C8,C9,C10,C11,C12,C13,C16	100nF/25V CERAMIC SMD SIZE 0805	YAGEO/MURATA	DIGIKEY
5	2	C14,C15	10uF/25V CERAMIC SMD SIZE 0805	YAGEO/MURATA	DIGIKEY
6	6	C17,C18,C21,C24,C25,C27	22PF/25V CERAMIC SMD SIZE 0805	YAGEO/MURATA	DIGIKEY
7	4	C19,C22,C31,C32	2.2nF/25V CERAMIC SMD SIZE 0805	YAGEO/MURATA	DIGIKEY
8	4	C20,C23,C29,C30	8.2nF/25V CERAMIC SMD SIZE 0805	YAGEO/MURATA	DIGIKEY
9	2	C26,C28	27nF/25V CERAMIC SMD SIZE 0805	YAGEO/MURATA	DIGIKEY
11	1	D1	LED RED SMD SIZE 0805	OSRAM	DIGIKEY	475-1278-1-ND
12	2	L1,L2	FERRITE BEAD 600OHMS SMD SIZE 0805	LAIRD	DIGIKEY	240-2390-1-ND
13	1	R1	2.2K 5% SMD SIZE 0805	YAGEO/MURATA	DIGIKEY
14	4	R2,R3,R16,R17	200E 5% SMD SIZE 0805	YAGEO/MURATA	DIGIKEY
15	4	R4,R8,R18,R19	820E 5% SMD SIZE 0805	YAGEO/MURATA	DIGIKEY
16	4	R5,R9,R12,R14	220E 5% SMD SIZE 0805	YAGEO/MURATA	DIGIKEY
17	4	R6,R10,R13,R15	180E 5% SMD SIZE 0805	YAGEO/MURATA	DIGIKEY
18	2	R7,R11	100E 5% SMD SIZE 0805	YAGEO/MURATA	DIGIKEY
19	6	U1,U2,U3,U4,U5,U6	NE5534 SOICS8	TI	DIGIKEY	296-16943-1-ND